Chapter 13 Mutual Affinities Of Organic Begins

Mutual¹ Affinities² Of Organic Begins: Morphology: Embryology: Rudimentary Organs


CLASSIFICATION, groups subordinate to groups. Natural system. Rules and difficulties in classification, explained on the theory of descent with modification⁶. Classification of varieties. Descent always used in classification. Analogical or adaptive characters. Affinities, general, complex and radiating. Extinction⁷ separates and defines groups. MORPHOLOGY, between members of the same class, between parts of the same individual. EMBRYOLOGY, laws of, explained by variations not supervening at an early age, and being inherited at a corresponding age. RUDIMENTARY ORGANS; their origin explained. Summary.

From the first dawn of life, all organic beings are found to resemble each other in descending⁸ degrees, so that they can be classed in groups under groups. This classification is evidently not arbitrary like the grouping of the stars in constellations⁹. The existence of groups would have been of simple signification, if one group had been exclusively fitted to inhabit the land, and another the water; one to feed on flesh, another on vegetable matter, and so on; but the case is widely different in nature; for it is notorious how commonly members of even the same subgroup have different habits. In our second and fourth chapters, on Variation and on Natural Selection, I have attempted to show that it is the widely ranging, the much diffused¹⁰ and common, that is the dominant¹¹ species belonging to the larger genera, which vary most. The varieties, or incipient¹² species, thus produced ultimately become converted, as I believe, into new and distinct species; and these, on the principle of inheritance, tend to produce other new and dominant species. Consequently the groups which are now large, and which generally include many dominant species, tend to go on increasing indefinitely in size. I further attempted to show that from the varying descendants of each species trying to occupy as many and as different places as possible in the economy of nature, there is a constant tendency in their characters to diverge¹³. This conclusion was supported by looking at the great diversity of the forms of life which, in any small area, come into the closest competition, and by looking to certain facts in naturalisation.

I attempted also to show that there is a constant tendency in the forms which are increasing in number and diverging¹⁴ in character, to supplant¹⁵ and exterminate¹⁶ the less divergent, the less improved, and preceding forms. I request the reader to turn to the diagram illustrating¹⁷ the action, as formerly¹⁸ explained, of these several principles; and he will see that the inevitable¹⁹ result is that the modified descendants proceeding²⁰ from one progenitor²¹ become broken up into groups subordinate to groups. In the diagram each letter on the uppermost line may represent a genus including several species; and all the genera on this line form together one class, for all have descended²² from one ancient but unseen parent, and, consequently, have inherited something in common. But the three genera on the left hand have, on this same principle, much in common, and form a sub-family, distinct from that including the next two genera on the right hand, which diverged²³ from a common parent at the fifth stage of descent. These five genera have also much, though less, in common; and they form a family distinct from that including the three genera still further to the right hand, which diverged at a still earlier period. And all these genera, descended from (A), form an order distinct from the genera descended from (I). So that we here have many species descended from a single progenitor grouped into genera; and the genera are included in, or subordinate to, sub-families, families, and orders, all united into one class. Thus, the grand fact in natural history of the subordination of group under group, which, from its familiarity, does not always sufficiently²⁴ strike us, is in my judgment²⁵ fully²⁶ explained.

Naturalists²⁸ try to arrange the species, genera, and families in each class, on what is called the Natural System. But what is meant by this system? Some authors look at it merely as a scheme for arranging together those living objects which are most alike, and for separating those which are most unlike; or as an artificial means for enunciating, as briefly³⁰ as possible, general propositions,--that is, by one sentence to give the characters common, for instance, to all mammals, by another those common to all carnivora, by another those common to the dog-genus, and then by adding a single sentence, a full description is given of each kind of dog. The ingenuity³¹ and utility of this system are indisputable. But many naturalists think that something more is meant by the Natural System; they believe that it reveals the plan of the Creator; but unless it be specified³² whether order in time or space, or what else is meant by the plan of the Creator, it seems to me that nothing is thus added to our knowledge. Such expressions as that famous one of Linnaeus, and which we often meet with in a more or less concealed³⁴ form, that the characters do not make the genus, but that the genus gives the characters, seem to imply that something more is included in our classification, than mere²⁹ resemblance. I believe that something more is included; and that propinquity of descent,--the only known cause of the similarity of organic beings,--is the bond, hidden as it is by various degrees of modification, which is partially³⁵ revealed to us by our classifications.

Let us now consider the rules followed in classification, and the difficulties which are encountered on the view that classification either gives some unknown plan of creation, or is simply a scheme for enunciating general propositions and of placing together the forms most like each other. It might have been thought (and was in ancient times thought) that those parts of the structure which determined³⁶ the habits of life, and the general place of each being in the economy of nature, would be of very high importance in classification. Nothing can be more false. No one regards the external similarity of a mouse to a shrew, of a dugong to a whale, of a whale to a fish, as of any importance. These resemblances, though so intimately connected with the whole life of the being, are ranked as merely "adaptive or analogical characters;" but to the consideration of these resemblances we shall have to recur³⁷. It may even be given as a general rule, that the less any part of the organisation³⁸ is concerned with special habits, the more important it becomes for classification. As an instance: Owen, in speaking of the dugong, says, "The generative organs being those which are most remotely related to the habits and food of an animal, I have always regarded as affording very clear indications of its true affinities. We are least likely in the modifications³⁹ of these organs to mistake a merely adaptive for an essential character." So with plants, how remarkable⁴⁰ it is that the organs of vegetation, on which their whole life depends, are of little signification, excepting in the first main divisions; whereas the organs of reproduction, with their product the seed, are of paramount⁴¹ importance!

We must not, therefore, in classifying, trust to resemblances in parts of the organisation, however important they may be for the welfare of the being in relation to the outer world. Perhaps from this cause it has partly arisen, that almost all naturalists lay the greatest stress on resemblances in organs of high vital or physiological⁴² importance. No doubt this view of the classificatory importance of organs which are important is generally, but by no means always, true. But their importance for classification, I believe, depends on their greater constancy throughout large groups of species; and this constancy depends on such organs having generally been subjected to less change in the adaptation of the species to their conditions of life. That the mere physiological importance of an organ does not determine its classificatory value, is almost shown by the one fact, that in allied⁴³ groups, in which the same organ, as we have every reason to suppose, has nearly the same physiological value, its classificatory value is widely different. No naturalist²⁷ can have worked at any group without being struck with this fact; and it has been most fully acknowledged in the writings of almost every author. It will suffice to quote the highest authority, Robert Brown, who in speaking of certain organs in the Proteaceae, says their generic⁴⁴ importance, "like that of all their parts, not only in this but, as I apprehend⁴⁵, in every natural family, is very unequal, and in some cases seems to be entirely⁴⁶ lost." Again in another work he says, the genera of the Connaraceae "differ in having one or more ovaria, in the existence or absence of albumen, in the imbricate or valvular aestivation. Any one of these characters singly is frequently of more than generic importance, though here even when all taken together they appear insufficient⁴⁷ to separate Cnestis from Connarus." To give an example amongst insects, in one great division of the Hymenoptera, the antennae⁴⁸, as Westwood has remarked, are most constant in structure; in another division they differ much, and the differences are of quite subordinate value in classification; yet no one probably will say that the antennae in these two divisions of the same order are of unequal physiological importance. Any number of instances could be given of the varying importance for classification of the same important organ within the same group of beings.

Again, no one will say that rudimentary or atrophied⁴⁹ organs are of high physiological or vital importance; yet, undoubtedly⁵⁰, organs in this condition are often of high value in classification. No one will dispute that the rudimentary teeth in the upper jaws⁵² of young ruminants, and certain rudimentary bones of the leg, are highly serviceable in exhibiting the close affinity⁵³ between Ruminants and Pachyderms. Robert Brown has strongly insisted on the fact that the rudimentary florets are of the highest importance in the classification of the Grasses.

Numerous instances could be given of characters derived⁵⁴ from parts which must be considered of very trifling⁵⁵ physiological importance, but which are universally admitted as highly serviceable in the definition of whole groups. For instance, whether or not there is an open passage from the nostrils⁵⁷ to the mouth, the only character, according to Owen, which absolutely distinguishes fishes and reptiles⁵⁸--the inflection of the angle of the jaws in Marsupials--the manner in which the wings of insects are folded--mere colour in certain Algae--mere pubescence on parts of the flower in grasses--the nature of the dermal⁶¹ covering, as hair or feathers, in the Vertebrata. If the Ornithorhynchus had been covered with feathers instead of hair, this external and trifling character would, I think, have been considered by naturalists as important an aid in determining the degree of affinity of this strange creature to birds and reptiles, as an approach in structure in any one internal and important organ.

The importance, for classification, of trifling characters, mainly depends on their being correlated with several other characters of more or less importance. The value indeed of an aggregate⁶² of characters is very evident in natural history. Hence, as has often been remarked, a species may depart from its allies in several characters, both of high physiological importance and of almost universal prevalence, and yet leave us in no doubt where it should be ranked. Hence, also, it has been found, that a classification founded on any single character, however important that may be, has always failed; for no part of the organisation is universally constant. The importance of an aggregate of characters, even when none are important, alone explains, I think, that saying of Linnaeus, that the characters do not give the genus, but the genus gives the characters; for this saying seems founded on an appreciation⁶³ of many trifling points of resemblance, too slight to be defined. Certain plants, belonging to the Malpighiaceae, bear perfect and degraded flowers; in the latter, as A. de Jussieu has remarked, "the greater number of the characters proper to the species, to the genus, to the family, to the class, disappear, and thus laugh at our classification." But when Aspicarpa produced in France, during several years, only degraded flowers, departing so wonderfully in a number of the most important points of structure from the proper type of the order, yet M. Richard sagaciously saw, as Jussieu observes, that this genus should still be retained amongst the Malpighiaceae. This case seems to me well to illustrate⁶⁴ the spirit with which our classifications are sometimes necessarily founded.

Practically when naturalists are at work, they do not trouble themselves about the physiological value of the characters which they use in defining a group, or in allocating⁶⁵ any particular species. If they find a character nearly uniform, and common to a great number of forms, and not common to others, they use it as one of high value; if common to some lesser⁶⁶ number, they use it as of subordinate value. This principle has been broadly confessed by some naturalists to be the true one; and by none more clearly than by that excellent botanist⁶⁷, Aug. St. Hilaire. If certain characters are always found correlated with others, though no apparent bond of connexion can be discovered between them, especial value is set on them. As in most groups of animals, important organs, such as those for propelling the blood, or for aerating⁶⁸ it, or those for propagating the race, are found nearly uniform, they are considered as highly serviceable in classification; but in some groups of animals all these, the most important vital organs, are found to offer characters of quite subordinate value.

We can see why characters derived from the embryo⁴ should be of equal importance with those derived from the adult, for our classifications of course include all ages of each species. But it is by no means obvious, on the ordinary view, why the structure of the embryo should be more important for this purpose than that of the adult, which alone plays its full part in the economy of nature. Yet it has been strongly urged by those great naturalists, Milne Edwards and Agassiz, that embryonic⁶⁹ characters are the most important of any in the classification of animals; and this doctrine⁷⁰ has very generally been admitted as true. The same fact holds good with flowering plants, of which the two main divisions have been founded on characters derived from the embryo,--on the number and position of the embryonic leaves or cotyledons, and on the mode of development of the plumule and radicle. In our discussion on embryology, we shall see why such characters are so valuable, on the view of classification tacitly including the idea of descent.

Our classifications are often plainly influenced by chains of affinities. Nothing can be easier than to define a number of characters common to all birds; but in the case of crustaceans⁷², such definition has hitherto been found impossible. There are crustaceans at the opposite ends of the series, which have hardly a character in common; yet the species at both ends, from being plainly allied to others, and these to others, and so onwards, can be recognised as unequivocally belonging to this, and to no other class of the Articulata.

Geographical⁷³ distribution has often been used, though perhaps not quite logically, in classification, more especially in very large groups of closely allied forms. Temminck insists on the utility or even necessity of this practice in certain groups of birds; and it has been followed by several entomologists and botanists⁷⁵.

Finally, with respect to the comparative value of the various groups of species, such as orders, sub-orders, families, sub-families, and genera, they seem to be, at least at present, almost arbitrary. Several of the best botanists, such as Mr. Bentham and others, have strongly insisted on their arbitrary value. Instances could be given amongst plants and insects, of a group of forms, first ranked by practised naturalists as only a genus, and then raised to the rank of a sub-family or family; and this has been done, not because further research has detected important structural⁷⁶ differences, at first overlooked, but because numerous allied species, with slightly different grades of difference, have been subsequently discovered.

All the foregoing rules and aids and difficulties in classification are explained, if I do not greatly deceive myself, on the view that the natural system is founded on descent with modification; that the characters which naturalists consider as showing true affinity between any two or more species, are those which have been inherited from a common parent, and, in so far, all true classification is genealogical; that community of descent is the hidden bond which naturalists have been unconsciously seeking, and not some unknown plan of creation, or the enunciation⁷⁸ of general propositions, and the mere putting together and separating objects more or less alike.

But I must explain my meaning more fully. I believe that the ARRANGEMENT of the groups within each class, in due subordination and relation to the other groups, must be strictly⁷⁹ genealogical in order to be natural; but that the AMOUNT of difference in the several branches or groups, though allied in the same degree in blood to their common progenitor, may differ greatly, being due to the different degrees of modification which they have undergone; and this is expressed by the forms being ranked under different genera, families, sections, or orders. The reader will best understand what is meant, if he will take the trouble of referring to the diagram in the fourth chapter. We will suppose the letters A to L to represent allied genera, which lived during the Silurian epoch⁸¹, and these have descended from a species which existed at an unknown anterior⁸² period. Species of three of these genera (A, F, and I) have transmitted modified descendants to the present day, represented by the fifteen genera (a14 to z14) on the uppermost horizontal line. Now all these modified descendants from a single species, are represented as related in blood or descent to the same degree; they may metaphorically⁸³ be called cousins to the same millionth degree; yet they differ widely and in different degrees from each other. The forms descended from A, now broken up into two or three families, constitute a distinct order from those descended from I, also broken up into two families. Nor can the existing species, descended from A, be ranked in the same genus with the parent A; or those from I, with the parent I. But the existing genus F14 may be supposed to have been but slightly modified; and it will then rank with the parent-genus F; just as some few still living organic beings belong to Silurian genera. So that the amount or value of the differences between organic beings all related to each other in the same degree in blood, has come to be widely different. Nevertheless their genealogical ARRANGEMENT remains⁸⁵ strictly true, not only at the present time, but at each successive period of descent. All the modified descendants from A will have inherited something in common from their common parent, as will all the descendants from I; so will it be with each subordinate branch of descendants, at each successive period. If, however, we choose to suppose that any of the descendants of A or of I have been so much modified as to have more or less completely lost traces of their parentage, in this case, their places in a natural classification will have been more or less completely lost,--as sometimes seems to have occurred with existing organisms. All the descendants of the genus F, along its whole line of descent, are supposed to have been but little modified, and they yet form a single genus. But this genus, though much isolated⁸⁶, will still occupy its proper intermediate position; for F originally was intermediate in character between A and I, and the several genera descended from these two genera will have inherited to a certain extent their characters. This natural arrangement is shown, as far as is possible on paper, in the diagram, but in much too simple a manner. If a branching diagram had not been used, and only the names of the groups had been written in a linear series, it would have been still less possible to have given a natural arrangement; and it is notoriously not possible to represent in a series, on a flat surface, the affinities which we discover in nature amongst the beings of the same group. Thus, on the view which I hold, the natural system is genealogical in its arrangement, like a pedigree; but the degrees of modification which the different groups have undergone, have to be expressed by ranking them under different so-called genera, sub-families, families, sections, orders, and classes.

It may be worth while to illustrate this view of classification, by taking the case of languages. If we possessed⁸⁷ a perfect pedigree of mankind, a genealogical arrangement of the races of man would afford the best classification of the various languages now spoken throughout the world; and if all extinct languages, and all intermediate and slowly changing dialects, had to be included, such an arrangement would, I think, be the only possible one. Yet it might be that some very ancient language had altered little, and had given rise to few new languages, whilst others (owing to the spreading and subsequent isolation⁸⁸ and states of civilisation⁸⁹ of the several races, descended from a common race) had altered much, and had given rise to many new languages and dialects. The various degrees of difference in the languages from the same stock, would have to be expressed by groups subordinate to groups; but the proper or even only possible arrangement would still be genealogical; and this would be strictly natural, as it would connect together all languages, extinct and modern, by the closest affinities, and would give the filiation and origin of each tongue.

In confirmation⁹⁰ of this view, let us glance at the classification of varieties, which are believed or known to have descended from one species. These are grouped under species, with sub-varieties under varieties; and with our domestic productions, several other grades of difference are requisite⁹¹, as we have seen with pigeons. The origin of the existence of groups subordinate to groups, is the same with varieties as with species, namely, closeness of descent with various degrees of modification. Nearly the same rules are followed in classifying varieties, as with species. Authors have insisted on the necessity of classing varieties on a natural instead of an artificial system; we are cautioned, for instance, not to class two varieties of the pine-apple together, merely because their fruit, though the most important part, happens to be nearly identical; no one puts the swedish and common turnips⁹² together, though the esculent and thickened stems are so similar. Whatever part is found to be most constant, is used in classing varieties: thus the great agriculturist Marshall says the horns are very useful for this purpose with cattle, because they are less variable than the shape or colour of the body, etc.; whereas with sheep the horns are much less serviceable, because less constant. In classing varieties, I apprehend if we had a real pedigree, a genealogical classification would be universally preferred; and it has been attempted by some authors. For we might feel sure, whether there had been more or less modification, the principle of inheritance would keep the forms together which were allied in the greatest number of points. In tumbler pigeons, though some sub-varieties differ from the others in the important character of having a longer beak⁹⁴, yet all are kept together from having the common habit of tumbling; but the short-faced breed has nearly or quite lost this habit; nevertheless, without any reasoning or thinking on the subject, these tumblers are kept in the same group, because allied in blood and alike in some other respects. If it could be proved that the Hottentot had descended from the Negro, I think he would be classed under the Negro group, however much he might differ in colour and other important characters from negroes.

With species in a state of nature, every naturalist has in fact brought descent into his classification; for he includes in his lowest grade, or that of a species, the two sexes; and how enormously these sometimes differ in the most important characters, is known to every naturalist: scarcely a single fact can be predicated in common of the males and hermaphrodites of certain cirripedes, when adult, and yet no one dreams of separating them. The naturalist includes as one species the several larval stages of the same individual, however much they may differ from each other and from the adult; as he likewise includes the so-called alternate generations of Steenstrup, which can only in a technical sense be considered as the same individual. He includes monsters; he includes varieties, not solely⁹⁵ because they closely resemble the parent-form, but because they are descended from it. He who believes that the cowslip is descended from the primrose⁹⁶, or conversely, ranks them together as a single species, and gives a single definition. As soon as three Orchidean forms (Monochanthus, Myanthus, and Catasetum), which had previously⁹⁷ been ranked as three distinct genera, were known to be sometimes produced on the same spike⁹⁸, they were immediately included as a single species. But it may be asked, what ought we to do, if it could be proved that one species of kangaroo had been produced, by a long course of modification, from a bear? Ought we to rank this one species with bears, and what should we do with the other species? The supposition is of course preposterous¹⁰⁰; and I might answer by the argumentum ad hominem, and ask what should be done if a perfect kangaroo were seen to come out of the womb of a bear? According to all analogy, it would be ranked with bears; but then assuredly all the other species of the kangaroo family would have to be classed under the bear genus. The whole case is preposterous; for where there has been close descent in common, there will certainly be close resemblance or affinity.

As descent has universally been used in classing together the individuals of the same species, though the males and females and larvae¹⁰¹ are sometimes extremely different; and as it has been used in classing varieties which have undergone a certain, and sometimes a considerable amount of modification, may not this same element of descent have been unconsciously used in grouping species under genera, and genera under higher groups, though in these cases the modification has been greater in degree, and has taken a longer time to complete? I believe it has thus been unconsciously used; and only thus can I understand the several rules and guides which have been followed by our best systematists. We have no written pedigrees; we have to make out community of descent by resemblances of any kind. Therefore we choose those characters which, as far as we can judge, are the least likely to have been modified in relation to the conditions of life to which each species has been recently exposed. Rudimentary structures on this view are as good as, or even sometimes better than, other parts of the organisation. We care not how trifling a character may be--let it be the mere inflection of the angle of the jaw⁵¹, the manner in which an insect's wing is folded, whether the skin be covered by hair or feathers--if it prevail throughout many and different species, especially those having very different habits of life, it assumes high value; for we can account for its presence in so many forms with such different habits, only by its inheritance from a common parent. We may err⁸⁰ in this respect in regard to single points of structure, but when several characters, let them be ever so trifling, occur together throughout a large group of beings having different habits, we may feel almost sure, on the theory of descent, that these characters have been inherited from a common ancestor. And we know that such correlated or aggregated¹⁰³ characters have especial value in classification.

We can understand why a species or a group of species may depart, in several of its most important characteristics, from its allies, and yet be safely classed with them. This may be safely done, and is often done, as long as a sufficient number of characters, let them be ever so unimportant, betrays the hidden bond of community of descent. Let two forms have not a single character in common, yet if these extreme forms are connected together by a chain of intermediate groups, we may at once infer their community of descent, and we put them all into the same class. As we find organs of high physiological importance--those which serve to preserve life under the most diverse conditions of existence--are generally the most constant, we attach especial value to them; but if these same organs, in another group or section of a group, are found to differ much, we at once value them less in our classification. We shall hereafter, I think, clearly see why embryological characters are of such high classificatory importance. Geographical distribution may sometimes be brought usefully into play in classing large and widely-distributed genera, because all the species of the same genus, inhabiting any distinct and isolated region, have in all probability descended from the same parents.

We can understand, on these views, the very important distinction between real affinities and analogical or adaptive resemblances. Lamarck first called attention to this distinction, and he has been ably followed by Macleay and others. The resemblance, in the shape of the body and in the fin³-like anterior limbs, between the dugong, which is a pachydermatous animal, and the whale, and between both these mammals and fishes, is analogical. Amongst insects there are innumerable instances: thus Linnaeus, misled by external appearances, actually classed an homopterous insect as a moth¹⁰⁴. We see something of the same kind even in our domestic varieties, as in the thickened stems of the common and swedish turnip⁹³. The resemblance of the greyhound and racehorse is hardly more fanciful than the analogies which have been drawn¹⁰⁵ by some authors between very distinct animals. On my view of characters being of real importance for classification, only in so far as they reveal descent, we can clearly understand why analogical or adaptive character, although of the utmost importance to the welfare of the being, are almost valueless to the systematist¹⁰². For animals, belonging to two most distinct lines of descent, may readily become adapted to similar conditions, and thus assume a close external resemblance; but such resemblances will not reveal--will rather tend to conceal³³ their blood-relationship to their proper lines of descent. We can also understand the apparent paradox¹⁰⁶, that the very same characters are analogical when one class or order is compared with another, but give true affinities when the members of the same class or order are compared one with another: thus the shape of the body and fin-like limbs are only analogical when whales are compared with fishes, being adaptations in both classes for swimming through the water; but the shape of the body and fin-like limbs serve as characters exhibiting true affinity between the several members of the whale family; for these cetaceans agree in so many characters, great and small, that we cannot doubt that they have inherited their general shape of body and structure of limbs from a common ancestor. So it is with fishes.

As members of distinct classes have often been adapted by successive slight modifications to live under nearly similar circumstances,--to inhabit for instance the three elements of land, air, and water,--we can perhaps understand how it is that a numerical parallelism has sometimes been observed between the sub-groups in distinct classes. A naturalist, struck by a parallelism of this nature in any one class, by arbitrarily raising or sinking the value of the groups in other classes (and all our experience shows that this valuation has hitherto been arbitrary), could easily extend the parallelism over a wide range; and thus the septenary, quinary, quaternary, and ternary classifications have probably arisen.

As the modified descendants of dominant species, belonging to the larger genera, tend to inherit the advantages, which made the groups to which they belong large and their parents dominant, they are almost sure to spread widely, and to seize on more and more places in the economy of nature. The larger and more dominant groups thus tend to go on increasing in size; and they consequently supplant many smaller and feebler groups. Thus we can account for the fact that all organisms, recent and extinct, are included under a few great orders, under still fewer classes, and all in one great natural system. As showing how few the higher groups are in number, and how widely spread they are throughout the world, the fact is striking, that the discovery of Australia has not added a single insect belonging to a new order; and that in the vegetable kingdom, as I learn from Dr. Hooker, it has added only two or three orders of small size.

In the chapter on geological succession I attempted to show, on the principle of each group having generally diverged much in character during the long-continued process of modification, how it is that the more ancient forms of life often present characters in some slight degree intermediate between existing groups. A few old and intermediate parent-forms having occasionally transmitted to the present day descendants but little modified, will give to us our so-called osculant or aberrant¹⁰⁷ groups. The more aberrant any form is, the greater must be the number of connecting forms which on my theory have been exterminated¹⁰⁸ and utterly¹⁰⁹ lost. And we have some evidence of aberrant forms having suffered severely¹¹⁰ from extinction, for they are generally represented by extremely few species; and such species as do occur are generally very distinct from each other, which again implies extinction. The genera Ornithorhynchus and Lepidosiren, for example, would not have been less aberrant had each been represented by a dozen species instead of by a single one; but such richness in species, as I find after some investigation¹¹¹, does not commonly fall to the lot of aberrant genera. We can, I think, account for this fact only by looking at aberrant forms as failing groups conquered by more successful competitors, with a few members preserved by some unusual coincidence of favourable¹¹² circumstances.

Mr. Waterhouse has remarked that, when a member belonging to one group of animals exhibits an affinity to a quite distinct group, this affinity in most cases is general and not special: thus, according to Mr. Waterhouse, of all Rodents¹¹³, the bizcacha is most nearly related to Marsupials; but in the points in which it approaches this order, its relations are general, and not to any one marsupial⁶⁰ species more than to another. As the points of affinity of the bizcacha to Marsupials are believed to be real and not merely adaptive, they are due on my theory to inheritance in common. Therefore we must suppose either that all Rodents, including the bizcacha, branched off from some very ancient Marsupial, which will have had a character in some degree intermediate with respect to all existing Marsupials; or that both Rodents and Marsupials branched off from a common progenitor, and that both groups have since undergone much modification in divergent directions. On either view we may suppose that the bizcacha has retained, by inheritance, more of the character of its ancient progenitor than have other Rodents; and therefore it will not be specially⁷⁴ related to any one existing Marsupial, but indirectly¹¹⁵ to all or nearly all Marsupials, from having partially retained the character of their common progenitor, or of an early member of the group. On the other hand, of all Marsupials, as Mr. Waterhouse has remarked, the phascolomys resembles most nearly, not any one species, but the general order of Rodents. In this case, however, it may be strongly suspected that the resemblance is only analogical, owing to the phascolomys having become adapted to habits like those of a Rodent¹¹⁴. The elder De Candolle has made nearly similar observations on the general nature of the affinities of distinct orders of plants.

On the principle of the multiplication¹¹⁶ and gradual divergence¹¹⁷ in character of the species descended from a common parent, together with their retention¹¹⁸ by inheritance of some characters in common, we can understand the excessively complex and radiating affinities by which all the members of the same family or higher group are connected together. For the common parent of a whole family of species, now broken up by extinction into distinct groups and sub-groups, will have transmitted some of its characters, modified in various ways and degrees, to all; and the several species will consequently be related to each other by circuitous¹¹⁹ lines of affinity of various lengths (as may be seen in the diagram so often referred to), mounting up through many predecessors¹²⁰. As it is difficult to show the blood-relationship between the numerous kindred of any ancient and noble family, even by the aid of a genealogical tree, and almost impossible to do this without this aid, we can understand the extraordinary difficulty which naturalists have experienced in describing, without the aid of a diagram, the various affinities which they perceive between the many living and extinct members of the same great natural class.

Extinction, as we have seen in the fourth chapter, has played an important part in defining and widening the intervals¹²¹ between the several groups in each class. We may thus account even for the distinctness of whole classes from each other--for instance, of birds from all other vertebrate animals--by the belief that many ancient forms of life have been utterly lost, through which the early progenitors¹²² of birds were formerly connected with the early progenitors of the other vertebrate classes. There has been less entire extinction of the forms of life which once connected fishes with batrachians. There has been still less in some other classes, as in that of the Crustacea, for here the most wonderfully diverse forms are still tied together by a long, but broken, chain of affinities. Extinction has only separated groups: it has by no means made them; for if every form which has ever lived on this earth were suddenly to reappear, though it would be quite impossible to give definitions by which each group could be distinguished¹²³ from other groups, as all would blend together by steps as fine as those between the finest existing varieties, nevertheless a natural classification, or at least a natural arrangement, would be possible. We shall see this by turning to the diagram: the letters, A to L, may represent eleven Silurian genera, some of which have produced large groups of modified descendants. Every intermediate link between these eleven genera and their primordial¹²⁴ parent, and every intermediate link in each branch and sub-branch of their descendants, may be supposed to be still alive; and the links to be as fine as those between the finest varieties. In this case it would be quite impossible to give any definition by which the several members of the several groups could be distinguished from their more immediate⁹⁹ parents; or these parents from their ancient and unknown progenitor. Yet the natural arrangement in the diagram would still hold good; and, on the principle of inheritance, all the forms descended from A, or from I, would have something in common. In a tree we can specify¹²⁵ this or that branch, though at the actual fork the two unite and blend together. We could not, as I have said, define the several groups; but we could pick out types, or forms, representing most of the characters of each group, whether large or small, and thus give a general idea of the value of the differences between them. This is what we should be driven to, if we were ever to succeed in collecting all the forms in any class which have lived throughout all time and space. We shall certainly never succeed in making so perfect a collection: nevertheless, in certain classes, we are tending in this direction; and Milne Edwards has lately insisted, in an able paper, on the high importance of looking to types, whether or not we can separate and define the groups to which such types belong.

Finally, we have seen that natural selection, which results from the struggle for existence, and which almost inevitably¹²⁶ induces extinction and divergence of character in the many descendants from one dominant parent-species, explains that great and universal feature in the affinities of all organic beings, namely, their subordination in group under group. We use the element of descent in classing the individuals of both sexes and of all ages, although having few characters in common, under one species; we use descent in classing acknowledged varieties, however different they may be from their parent; and I believe this element of descent is the hidden bond of connexion which naturalists have sought under the term of the Natural System. On this idea of the natural system being, in so far as it has been perfected, genealogical in its arrangement, with the grades of difference between the descendants from a common parent, expressed by the terms genera, families, orders, etc., we can understand the rules which we are compelled to follow in our classification. We can understand why we value certain resemblances far more than others; why we are permitted to use rudimentary and useless organs, or others of trifling physiological importance; why, in comparing one group with a distinct group, we summarily reject analogical or adaptive characters, and yet use these same characters within the limits of the same group. We can clearly see how it is that all living and extinct forms can be grouped together in one great system; and how the several members of each class are connected together by the most complex and radiating lines of affinities. We shall never, probably, disentangle the inextricable web of affinities between the members of any one class; but when we have a distinct object in view, and do not look to some unknown plan of creation, we may hope to make sure but slow progress.

MORPHOLOGY.

We have seen that the members of the same class, independently of their habits of life, resemble each other in the general plan of their organisation. This resemblance is often expressed by the term "unity⁷⁷ of type;" or by saying that the several parts and organs in the different species of the class are homologous. The whole subject is included under the general name of Morphology. This is the most interesting department of natural history, and may be said to be its very soul. What can be more curious than that the hand of a man, formed for grasping, that of a mole¹²⁷ for digging, the leg of the horse, the paddle of the porpoise¹²⁸, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions? Geoffroy St. Hilaire has insisted strongly on the high importance of relative connexion in homologous organs: the parts may change to almost any extent in form and size, and yet they always remain connected together in the same order. We never find, for instance, the bones of the arm and forearm, or of the thigh¹²⁹ and leg, transposed. Hence the same names can be given to the homologous bones in widely different animals. We see the same great law in the construction of the mouths of insects: what can be more different than the immensely long spiral proboscis¹³⁰ of a sphinx-moth, the curious folded one of a bee or bug¹³¹, and the great jaws of a beetle¹³²?--yet all these organs, serving for such different purposes, are formed by infinitely¹³³ numerous modifications of an upper lip, mandibles, and two pairs of maxillae. Analogous¹³⁴ laws govern the construction of the mouths and limbs of crustaceans. So it is with the flowers of plants.

Nothing can be more hopeless than to attempt to explain this similarity of pattern in members of the same class, by utility or by the doctrine of final causes. The hopelessness of the attempt has been expressly admitted by Owen in his most interesting work on the 'Nature of Limbs.' On the ordinary view of the independent creation of each being, we can only say that so it is;--that it has so pleased the Creator to construct each animal and plant.

The explanation is manifest on the theory of the natural selection of successive slight modifications,--each modification being profitable in some way to the modified form, but often affecting by correlation¹³⁵ of growth other parts of the organisation. In changes of this nature, there will be little or no tendency to modify the original pattern, or to transpose parts. The bones of a limb might be shortened and widened to any extent, and become gradually enveloped¹³⁶ in thick membrane¹³⁷, so as to serve as a fin; or a webbed foot might have all its bones, or certain bones, lengthened¹³⁸ to any extent, and the membrane connecting them increased to any extent, so as to serve as a wing: yet in all this great amount of modification there will be no tendency to alter the framework of bones or the relative connexion of the several parts. If we suppose that the ancient progenitor, the archetype as it may be called, of all mammals, had its limbs constructed on the existing general pattern, for whatever purpose they served, we can at once perceive the plain signification of the homologous construction of the limbs throughout the whole class. So with the mouths of insects, we have only to suppose that their common progenitor had an upper lip, mandibles, and two pair of maxillae, these parts being perhaps very simple in form; and then natural selection will account for the infinite diversity in structure and function of the mouths of insects. Nevertheless, it is conceivable that the general pattern of an organ might become so much obscured as to be finally lost, by the atrophy¹³⁹ and ultimately by the complete abortion¹⁴⁰ of certain parts, by the soldering¹⁴¹ together of other parts, and by the doubling or multiplication of others,--variations which we know to be within the limits of possibility. In the paddles of the extinct gigantic sea-lizards, and in the mouths of certain suctorial crustaceans, the general pattern seems to have been thus to a certain extent obscured.

There is another and equally curious branch of the present subject; namely, the comparison not of the same part in different members of a class, but of the different parts or organs in the same individual. Most physiologists¹⁴³ believe that the bones of the skull¹⁴⁴ are homologous with--that is correspond in number and in relative connexion with--the elemental parts of a certain number of vertebrae. The anterior and posterior limbs in each member of the vertebrate and articulate classes are plainly homologous. We see the same law in comparing the wonderfully complex jaws and legs in crustaceans. It is familiar to almost every one, that in a flower the relative position of the sepals, petals¹⁴⁵, stamens, and pistils, as well as their intimate structure, are intelligible¹⁴⁶ on the view that they consist of metamorphosed leaves, arranged in a spire¹⁴⁷. In monstrous¹⁴⁸ plants, we often get direct evidence of the possibility of one organ being transformed into another; and we can actually see in embryonic crustaceans and in many other animals, and in flowers, that organs, which when mature become extremely different, are at an early stage of growth exactly alike.

How inexplicable¹⁴⁹ are these facts on the ordinary view of creation! Why should the brain be enclosed in a box composed of such numerous and such extraordinarily¹⁵⁰ shaped pieces of bone? As Owen has remarked, the benefit derived from the yielding of the separate pieces in the act of parturition¹⁵¹ of mammals, will by no means explain the same construction in the skulls¹⁵² of birds. Why should similar bones have been created in the formation of the wing and leg of a bat, used as they are for such totally different purposes? Why should one crustacean⁷¹, which has an extremely complex mouth formed of many parts, consequently always have fewer legs; or conversely, those with many legs have simpler mouths? Why should the sepals, petals, stamens, and pistils in any individual flower, though fitted for such widely different purposes, be all constructed on the same pattern?

On the theory of natural selection, we can satisfactorily answer these questions. In the vertebrata, we see a series of internal vertebrae bearing certain processes and appendages¹⁵⁴; in the articulata, we see the body divided into a series of segments, bearing external appendages; and in flowering plants, we see a series of successive spiral whorls of leaves. An indefinite repetition of the same part or organ is the common characteristic (as Owen has observed) of all low or little-modified forms; therefore we may readily believe that the unknown progenitor of the vertebrata possessed many vertebrae; the unknown progenitor of the articulata, many segments; and the unknown progenitor of flowering plants, many spiral whorls of leaves. We have formerly seen that parts many times repeated are eminently¹⁵⁶ liable to vary in number and structure; consequently it is quite probable that natural selection, during a long-continued course of modification, should have seized on a certain number of the primordially¹⁵⁷ similar elements, many times repeated, and have adapted them to the most diverse purposes. And as the whole amount of modification will have been effected by slight successive steps, we need not wonder at discovering in such parts or organs, a certain degree of fundamental resemblance, retained by the strong principle of inheritance.

In the great class of molluscs, though we can homologise the parts of one species with those of another and distinct species, we can indicate but few serial¹⁵⁸ homologies; that is, we are seldom enabled to say that one part or organ is homologous with another in the same individual. And we can understand this fact; for in molluscs, even in the lowest members of the class, we do not find nearly so much indefinite repetition of any one part, as we find in the other great classes of the animal and vegetable kingdoms.

Naturalists frequently speak of the skull as formed of metamorphosed vertebrae: the jaws of crabs¹⁶⁰ as metamorphosed legs; the stamens and pistils of flowers as metamorphosed leaves; but it would in these cases probably be more correct, as Professor Huxley has remarked, to speak of both skull and vertebrae, both jaws and legs, etc.,--as having been metamorphosed, not one from the other, but from some common element. Naturalists, however, use such language only in a metaphorical⁸⁴ sense: they are far from meaning that during a long course of descent, primordial organs of any kind--vertebrae in the one case and legs in the other--have actually been modified into skulls or jaws. Yet so strong is the appearance of a modification of this nature having occurred, that naturalists can hardly avoid employing language having this plain signification. On my view these terms may be used literally¹⁶¹; and the wonderful fact of the jaws, for instance, of a crab¹⁵⁹ retaining numerous characters, which they would probably have retained through inheritance, if they had really been metamorphosed during a long course of descent from true legs, or from some simple appendage¹⁵³, is explained.

EMBRYOLOGY.

It has already been casually¹⁶² remarked that certain organs in the individual, which when mature become widely different and serve for different purposes, are in the embryo exactly alike. The embryos¹⁶³, also, of distinct animals within the same class are often strikingly similar: a better proof of this cannot be given, than a circumstance mentioned by Agassiz, namely, that having forgotten to ticket the embryo of some vertebrate animal, he cannot now tell whether it be that of a mammal, bird, or reptile⁵⁹. The vermiform larvae of moths¹⁶⁴, flies, beetles¹⁶⁵, etc., resemble each other much more closely than do the mature insects; but in the case of larvae, the embryos are active, and have been adapted for special lines of life. A trace of the law of embryonic resemblance, sometimes lasts till a rather late age: thus birds of the same genus, and of closely allied genera, often resemble each other in their first and second plumage; as we see in the spotted¹⁶⁶ feathers in the thrush group. In the cat tribe, most of the species are striped or spotted in lines; and stripes can be plainly distinguished in the whelp of the lion. We occasionally though rarely see something of this kind in plants: thus the embryonic leaves of the ulex or furze, and the first leaves of the phyllodineous acaceas, are pinnate or divided like the ordinary leaves of the leguminosae.

The points of structure, in which the embryos of widely different animals of the same class resemble each other, often have no direct relation to their conditions of existence. We cannot, for instance, suppose that in the embryos of the vertebrata the peculiar¹⁶⁷ loop-like course of the arteries¹⁶⁸ near the branchial slits¹⁶⁹ are related to similar conditions,--in the young mammal which is nourished in the womb of its mother, in the egg of the bird which is hatched in a nest, and in the spawn¹⁷⁰ of a frog under water. We have no more reason to believe in such a relation, than we have to believe that the same bones in the hand of a man, wing of a bat, and fin of a porpoise, are related to similar conditions of life. No one will suppose that the stripes on the whelp of a lion, or the spots on the young blackbird, are of any use to these animals, or are related to the conditions to which they are exposed.

The case, however, is different when an animal during any part of its embryonic career is active, and has to provide for itself. The period of activity may come on earlier or later in life; but whenever it comes on, the adaptation of the larva to its conditions of life is just as perfect and as beautiful as in the adult animal. From such special adaptations, the similarity of the larvae or active embryos of allied animals is sometimes much obscured; and cases could be given of the larvae of two species, or of two groups of species, differing quite as much, or even more, from each other than do their adult parents. In most cases, however, the larvae, though active, still obey more or less closely the law of common embryonic resemblance. Cirripedes afford a good instance of this: even the illustrious Cuvier did not perceive that a barnacle was, as it certainly is, a crustacean; but a glance at the larva shows this to be the case in an unmistakeable manner. So again the two main divisions of cirripedes, the pedunculated and sessile, which differ widely in external appearance, have larvae in all their several stages barely distinguishable.

The embryo in the course of development generally rises in organisation: I use this expression, though I am aware that it is hardly possible to define clearly what is meant by the organisation being higher or lower. But no one probably will dispute that the butterfly is higher than the caterpillar¹⁷¹. In some cases, however, the mature animal is generally considered as lower in the scale than the larva, as with certain parasitic¹⁷² crustaceans. To refer once again to cirripedes: the larvae in the first stage have three pairs of legs, a very simple single eye, and a probosciformed mouth, with which they feed largely, for they increase much in size. In the second stage, answering to the chrysalis stage of butterflies, they have six pairs of beautifully constructed natatory legs, a pair of magnificent compound eyes, and extremely complex antennae; but they have a closed and imperfect mouth, and cannot feed: their function at this stage is, to search by their well-developed organs of sense, and to reach by their active powers of swimming, a proper place on which to become attached and to undergo their final metamorphosis. When this is completed they are fixed¹⁷³ for life: their legs are now converted into prehensile¹⁷⁴ organs; they again obtain a well-constructed mouth; but they have no antennae, and their two eyes are now reconverted into a minute, single, and very simple eye-spot. In this last and complete state, cirripedes may be considered as either more highly or more lowly organised than they were in the larval condition. But in some genera the larvae become developed either into hermaphrodites having the ordinary structure, or into what I have called complemental¹⁷⁵ males: and in the latter, the development has assuredly been retrograde; for the male is a mere sack, which lives for a short time, and is destitute¹⁷⁶ of mouth, stomach, or other organ of importance, excepting for reproduction.

We are so much accustomed to see differences in structure between the embryo and the adult, and likewise a close similarity in the embryos of widely different animals within the same class, that we might be led to look at these facts as necessarily contingent¹⁷⁷ in some manner on growth. But there is no obvious reason why, for instance, the wing of a bat, or the fin of a porpoise, should not have been sketched¹⁷⁸ out with all the parts in proper proportion, as soon as any structure became visible in the embryo. And in some whole groups of animals and in certain members of other groups, the embryo does not at any period differ widely from the adult: thus Owen has remarked in regard to cuttle-fish, "there is no metamorphosis; the cephalopodic character is manifested long before the parts of the embryo are completed;" and again in spiders, "there is nothing worthy¹⁷⁹ to be called a metamorphosis." The larvae of insects, whether adapted to the most diverse and active habits, or quite inactive, being fed by their parents or placed in the midst of proper nutriment, yet nearly all pass through a similar worm-like stage of development; but in some few cases, as in that of Aphis, if we look to the admirable drawings by Professor Huxley of the development of this insect, we see no trace of the vermiform stage.

How, then, can we explain these several facts in embryology,--namely the very general, but not universal difference in structure between the embryo and the adult;--of parts in the same individual embryo, which ultimately become very unlike and serve for diverse purposes, being at this early period of growth alike;--of embryos of different species within the same class, generally, but not universally, resembling each other;--of the structure of the embryo not being closely related to its conditions of existence, except when the embryo becomes at any period of life active and has to provide for itself;--of the embryo apparently¹⁸⁰ having sometimes a higher organisation than the mature animal, into which it is developed. I believe that all these facts can be explained, as follows, on the view of descent with modification.

It is commonly assumed, perhaps from monstrosities often affecting the embryo at a very early period, that slight variations necessarily appear at an equally early period. But we have little evidence on this head--indeed the evidence rather points the other way; for it is notorious that breeders of cattle, horses, and various fancy animals, cannot positively¹⁸¹ tell, until some time after the animal has been born, what its merits or form will ultimately turn out. We see this plainly in our own children; we cannot always tell whether the child will be tall or short, or what its precise features will be. The question is not, at what period of life any variation has been caused, but at what period it is fully displayed. The cause may have acted, and I believe generally has acted, even before the embryo is formed; and the variation may be due to the male and female sexual elements having been affected¹⁸² by the conditions to which either parent, or their ancestors, have been exposed. Nevertheless an effect thus caused at a very early period, even before the formation of the embryo, may appear late in life; as when an hereditary¹⁸³ disease, which appears in old age alone, has been communicated to the offspring from the reproductive element of one parent. Or again, as when the horns of cross-bred cattle have been affected by the shape of the horns of either parent. For the welfare of a very young animal, as long as it remains in its mother's womb, or in the egg, or as long as it is nourished and protected by its parent, it must be quite unimportant whether most of its characters are fully acquired a little earlier or later in life. It would not signify, for instance, to a bird which obtained its food best by having a long beak, whether or not it assumed a beak of this particular length, as long as it was fed by its parents. Hence, I conclude, that it is quite possible, that each of the many successive modifications, by which each species has acquired its present structure, may have supervened at a not very early period of life; and some direct evidence from our domestic animals supports this view. But in other cases it is quite possible that each successive modification, or most of them, may have appeared at an extremely early period.

I have stated in the first chapter, that there is some evidence to render it probable, that at whatever age any variation first appears in the parent, it tends to reappear at a corresponding age in the offspring. Certain variations can only appear at corresponding ages, for instance, peculiarities¹⁸⁴ in the caterpillar, cocoon¹⁸⁵, or imago states of the silk-moth; or, again, in the horns of almost full-grown cattle. But further than this, variations which, for all that we can see, might have appeared earlier or later in life, tend to appear at a corresponding age in the offspring and parent. I am far from meaning that this is invariably the case; and I could give a good many cases of variations (taking the word in the largest sense) which have supervened at an earlier age in the child than in the parent.

These two principles, if their truth be admitted, will, I believe, explain all the above specified leading facts in embryology. But first let us look at a few analogous cases in domestic varieties. Some authors who have written on Dogs, maintain that the greyhound and bulldog, though appearing so different, are really varieties most closely allied, and have probably descended from the same wild stock; hence I was curious to see how far their puppies differed from each other: I was told by breeders that they differed just as much as their parents, and this, judging by the eye, seemed almost to be the case; but on actually measuring the old dogs and their six-days old puppies, I found that the puppies had not nearly acquired their full amount of proportional difference. So, again, I was told that the foals of cart and race-horses differed as much as the full-grown animals; and this surprised me greatly, as I think it probable that the difference between these two breeds has been wholly caused by selection under domestication¹⁸⁶; but having had careful measurements made of the dam and of a three-days old colt of a race and heavy cart-horse, I find that the colts have by no means acquired their full amount of proportional difference.

As the evidence appears to me conclusive¹⁸⁷, that the several domestic breeds of Pigeon have descended from one wild species, I compared young pigeons of various breeds, within twelve hours after being hatched; I carefully measured the proportions (but will not here give details) of the beak, width of mouth, length of nostril⁵⁶ and of eyelid¹⁸⁸, size of feet and length of leg, in the wild stock, in pouters, fantails, runts, barbs¹⁸⁹, dragons, carriers, and tumblers. Now some of these birds, when mature, differ so extraordinarily in length and form of beak, that they would, I cannot doubt, be ranked in distinct genera, had they been natural productions. But when the nestling birds of these several breeds were placed in a row, though most of them could be distinguished from each other, yet their proportional differences in the above specified several points were incomparably less than in the full-grown birds. Some characteristic points of difference--for instance, that of the width of mouth--could hardly be detected in the young. But there was one remarkable exception to this rule, for the young of the short-faced tumbler differed from the young of the wild rock-pigeon and of the other breeds, in all its proportions, almost exactly as much as in the adult state.

The two principles above given seem to me to explain these facts in regard to the later embryonic stages of our domestic varieties. Fanciers select their horses, dogs, and pigeons, for breeding, when they are nearly grown up: they are indifferent whether the desired qualities and structures have been acquired earlier or later in life, if the full-grown animal possesses them. And the cases just given, more especially that of pigeons, seem to show that the characteristic differences which give value to each breed, and which have been accumulated by man's selection, have not generally first appeared at an early period of life, and have been inherited by the offspring at a corresponding not early period. But the case of the short-faced tumbler, which when twelve hours old had acquired its proper proportions, proves that this is not the universal rule; for here the characteristic differences must either have appeared at an earlier period than usual, or, if not so, the differences must have been inherited, not at the corresponding, but at an earlier age.

Now let us apply these facts and the above two principles--which latter, though not proved true, can be shown to be in some degree probable--to species in a state of nature. Let us take a genus of birds, descended on my theory from some one parent-species, and of which the several new species have become modified through natural selection in accordance with their diverse habits. Then, from the many slight successive steps of variation having supervened at a rather late age, and having been inherited at a corresponding age, the young of the new species of our supposed genus will manifestly tend to resemble each other much more closely than do the adults, just as we have seen in the case of pigeons. We may extend this view to whole families or even classes. The fore-limbs, for instance, which served as legs in the parent-species, may become, by a long course of modification, adapted in one descendant to act as hands, in another as paddles, in another as wings; and on the above two principles--namely of each successive modification supervening at a rather late age, and being inherited at a corresponding late age--the fore-limbs in the embryos of the several descendants of the parent-species will still resemble each other closely, for they will not have been modified. But in each individual new species, the embryonic fore-limbs will differ greatly from the fore-limbs in the mature animal; the limbs in the latter having undergone much modification at a rather late period of life, and having thus been converted into hands, or paddles, or wings. Whatever influence long-continued exercise or use on the one hand, and disuse on the other, may have in modifying an organ, such influence will mainly affect the mature animal, which has come to its full powers of activity and has to gain its own living; and the effects thus produced will be inherited at a corresponding mature age. Whereas the young will remain unmodified, or be modified in a lesser degree, by the effects of use and disuse.

In certain cases the successive steps of variation might supervene, from causes of which we are wholly ignorant, at a very early period of life, or each step might be inherited at an earlier period than that at which it first appeared. In either case (as with the short-faced tumbler) the young or embryo would closely resemble the mature parent-form. We have seen that this is the rule of development in certain whole groups of animals, as with cuttle-fish and spiders, and with a few members of the great class of insects, as with Aphis. With respect to the final cause of the young in these cases not undergoing any metamorphosis, or closely resembling their parents from their earliest age, we can see that this would result from the two following contingencies¹⁹⁰; firstly, from the young, during a course of modification carried on for many generations, having to provide for their own wants at a very early stage of development, and secondly¹⁹¹, from their following exactly the same habits of life with their parents; for in this case, it would be indispensable for the existence of the species, that the child should be modified at a very early age in the same manner with its parents, in accordance with their similar habits. Some further explanation, however, of the embryo not undergoing any metamorphosis is perhaps requisite. If, on the other hand, it profited the young to follow habits of life in any degree different from those of their parent, and consequently to be constructed in a slightly different manner, then, on the principle of inheritance at corresponding ages, the active young or larvae might easily be rendered by natural selection different to any conceivable extent from their parents. Such differences might, also, become correlated with successive stages of development; so that the larvae, in the first stage, might differ greatly from the larvae in the second stage, as we have seen to be the case with cirripedes. The adult might become fitted for sites or habits, in which organs of locomotion¹⁹² or of the senses, etc., would be useless; and in this case the final metamorphosis would be said to be retrograde.

As all the organic beings, extinct and recent, which have ever lived on this earth have to be classed together, and as all have been connected by the finest gradations, the best, or indeed, if our collections were nearly perfect, the only possible arrangement, would be genealogical. Descent being on my view the hidden bond of connexion which naturalists have been seeking under the term of the natural system. On this view we can understand how it is that, in the eyes of most naturalists, the structure of the embryo is even more important for classification than that of the adult. For the embryo is the animal in its less modified state; and in so far it reveals the structure of its progenitor. In two groups of animal, however much they may at present differ from each other in structure and habits, if they pass through the same or similar embryonic stages, we may feel assured that they have both descended from the same or nearly similar parents, and are therefore in that degree closely related. Thus, community in embryonic structure reveals community of descent. It will reveal this community of descent, however much the structure of the adult may have been modified and obscured; we have seen, for instance, that cirripedes can at once be recognised by their larvae as belonging to the great class of crustaceans. As the embryonic state of each species and group of species partially shows us the structure of their less modified ancient progenitors, we can clearly see why ancient and extinct forms of life should resemble the embryos of their descendants,--our existing species. Agassiz believes this to be a law of nature; but I am bound to confess that I only hope to see the law hereafter proved true. It can be proved true in those cases alone in which the ancient state, now supposed to be represented in many embryos, has not been obliterated¹⁹³, either by the successive variations in a long course of modification having supervened at a very early age, or by the variations having been inherited at an earlier period than that at which they first appeared. It should also be borne in mind, that the supposed law of resemblance of ancient forms of life to the embryonic stages of recent forms, may be true, but yet, owing to the geological record not extending far enough back in time, may remain for a long period, or for ever, incapable¹⁹⁴ of demonstration¹⁹⁵.

Thus, as it seems to me, the leading facts in embryology, which are second in importance to none in natural history, are explained on the principle of slight modifications not appearing, in the many descendants from some one ancient progenitor, at a very early period in the life of each, though perhaps caused at the earliest, and being inherited at a corresponding not early period. Embryology rises greatly in interest, when we thus look at the embryo as a picture, more or less obscured, of the common parent-form of each great class of animals.

RUDIMENTARY, ATROPHIED, OR ABORTED¹⁹⁶ ORGANS.

Organs or parts in this strange condition, bearing the stamp of inutility, are extremely common throughout nature. For instance, rudimentary mammae are very general in the males of mammals: I presume that the "bastard-wing" in birds may be safely considered as a digit¹⁹⁷ in a rudimentary state: in very many snakes one lobe¹⁹⁸ of the lungs is rudimentary; in other snakes there are rudiments¹⁹⁹ of the pelvis and hind²⁰⁰ limbs. Some of the cases of rudimentary organs are extremely curious; for instance, the presence of teeth in foetal whales, which when grown up have not a tooth in their heads; and the presence of teeth, which never cut through the gums, in the upper jaws of our unborn calves²⁰¹. It has even been stated on good authority that rudiments of teeth can be detected in the beaks²⁰² of certain embryonic birds. Nothing can be plainer than that wings are formed for flight, yet in how many insects do we see wings so reduced in size as to be utterly incapable of flight, and not rarely lying under wing-cases, firmly soldered²⁰³ together!

The meaning of rudimentary organs is often quite unmistakeable: for instance there are beetles of the same genus (and even of the same species) resembling each other most closely in all respects, one of which will have full-sized wings, and another mere rudiments of membrane; and here it is impossible to doubt, that the rudiments represent wings. Rudimentary organs sometimes retain their potentiality, and are merely not developed: this seems to be the case with the mammae of male mammals, for many instances are on record of these organs having become well developed in full-grown males, and having secreted²⁰⁴ milk. So again there are normally four developed and two rudimentary teats in the udders of the genus Bos, but in our domestic cows the two sometimes become developed and give milk. In individual plants of the same species the petals sometimes occur as mere rudiments, and sometimes in a well-developed state. In plants with separated sexes, the male flowers often have a rudiment⁵ of a pistil; and Kolreuter found that by crossing such male plants with an hermaphrodite species, the rudiment of the pistil in the hybrid²⁰⁵ offspring was much increased in size; and this shows that the rudiment and the perfect pistil are essentially²⁰⁶ alike in nature.

An organ serving for two purposes, may become rudimentary or utterly aborted for one, even the more important purpose; and remain perfectly²⁰⁷ efficient for the other. Thus in plants, the office of the pistil is to allow the pollen²⁰⁸-tubes to reach the ovules protected in the ovarium at its base. The pistil consists of a stigma²⁰⁹ supported on the style; but in some Compositae, the male florets, which of course cannot be fecundated, have a pistil, which is in a rudimentary state, for it is not crowned with a stigma; but the style remains well developed, and is clothed with hairs as in other compositae, for the purpose of brushing the pollen out of the surrounding anthers. Again, an organ may become rudimentary for its proper purpose, and be used for a distinct object: in certain fish the swim-bladder seems to be rudimentary for its proper function of giving buoyancy, but has become converted into a nascent²¹⁰ breathing organ or lung. Other similar instances could be given.

Rudimentary organs in the individuals of the same species are very liable to vary in degree of development and in other respects. Moreover, in closely allied species, the degree to which the same organ has been rendered rudimentary occasionally differs much. This latter fact is well exemplified in the state of the wings of the female moths in certain groups. Rudimentary organs may be utterly aborted; and this implies, that we find in an animal or plant no trace of an organ, which analogy would lead us to expect to find, and which is occasionally found in monstrous individuals of the species. Thus in the snapdragon (antirrhinum) we generally do not find a rudiment of a fifth stamen; but this may sometimes be seen. In tracing the homologies of the same part in different members of a class, nothing is more common, or more necessary, than the use and discovery of rudiments. This is well shown in the drawings given by Owen of the bones of the leg of the horse, ox, and rhinoceros²¹¹.

It is an important fact that rudimentary organs, such as teeth in the upper jaws of whales and ruminants, can often be detected in the embryo, but afterwards wholly disappear. It is also, I believe, a universal rule, that a rudimentary part or organ is of greater size relatively²¹² to the adjoining parts in the embryo, than in the adult; so that the organ at this early age is less rudimentary, or even cannot be said to be in any degree rudimentary. Hence, also, a rudimentary organ in the adult, is often said to have retained its embryonic condition.

I have now given the leading facts with respect to rudimentary organs. In reflecting on them, every one must be struck with astonishment²¹³: for the same reasoning power which tells us plainly that most parts and organs are exquisitely²¹⁴ adapted for certain purposes, tells us with equal plainness that these rudimentary or atrophied organs, are imperfect and useless. In works on natural history rudimentary organs are generally said to have been created "for the sake of symmetry," or in order "to complete the scheme of nature;" but this seems to me no explanation, merely a restatement of the fact. Would it be thought sufficient to say that because planets revolve²¹⁵ in elliptic courses round the sun, satellites follow the same course round the planets, for the sake of symmetry, and to complete the scheme of nature? An eminent¹⁵⁵ physiologist¹⁴² accounts for the presence of rudimentary organs, by supposing that they serve to excrete matter in excess, or injurious to the system; but can we suppose that the minute papilla, which often represents the pistil in male flowers, and which is formed merely of cellular²¹⁶ tissue, can thus act? Can we suppose that the formation of rudimentary teeth which are subsequently absorbed, can be of any service to the rapidly growing embryonic calf²¹⁷ by the excretion of precious phosphate of lime? When a man's fingers have been amputated, imperfect nails sometimes appear on the stumps²¹⁹: I could as soon believe that these vestiges²²¹ of nails have appeared, not from unknown laws of growth, but in order to excrete horny matter, as that the rudimentary nails on the fin of the manatee²²² were formed for this purpose.

On my view of descent with modification, the origin of rudimentary organs is simple. We have plenty of cases of rudimentary organs in our domestic productions,--as the stump²¹⁸ of a tail in tailless breeds,--the vestige²²⁰ of an ear in earless breeds,--the reappearance of minute dangling²²³ horns in hornless breeds of cattle, more especially, according to Youatt, in young animals,--and the state of the whole flower in the cauliflower. We often see rudiments of various parts in monsters. But I doubt whether any of these cases throw light on the origin of rudimentary organs in a state of nature, further than by showing that rudiments can be produced; for I doubt whether species under nature ever undergo abrupt²²⁴ changes. I believe that disuse has been the main agency; that it has led in successive generations to the gradual reduction of various organs, until they have become rudimentary,--as in the case of the eyes of animals inhabiting dark caverns²²⁵, and of the wings of birds inhabiting oceanic islands, which have seldom been forced to take flight, and have ultimately lost the power of flying. Again, an organ useful under certain conditions, might become injurious under others, as with the wings of beetles living on small and exposed islands; and in this case natural selection would continue slowly to reduce the organ, until it was rendered harmless and rudimentary.

Any change in function, which can be effected by insensibly small steps, is within the power of natural selection; so that an organ rendered, during changed habits of life, useless or injurious for one purpose, might easily be modified and used for another purpose. Or an organ might be retained for one alone of its former functions. An organ, when rendered useless, may well be variable, for its variations cannot be checked by natural selection. At whatever period of life disuse or selection reduces an organ, and this will generally be when the being has come to maturity²²⁶ and to its full powers of action, the principle of inheritance at corresponding ages will reproduce the organ in its reduced state at the same age, and consequently will seldom affect or reduce it in the embryo. Thus we can understand the greater relative size of rudimentary organs in the embryo, and their lesser relative size in the adult. But if each step of the process of reduction were to be inherited, not at the corresponding age, but at an extremely early period of life (as we have good reason to believe to be possible) the rudimentary part would tend to be wholly lost, and we should have a case of complete abortion. The principle, also, of economy, explained in a former chapter, by which the materials forming any part or structure, if not useful to the possessor, will be saved as far as is possible, will probably often come into play; and this will tend to cause the entire obliteration²²⁷ of a rudimentary organ.

As the presence of rudimentary organs is thus due to the tendency in every part of the organisation, which has long existed, to be inherited--we can understand, on the genealogical view of classification, how it is that systematists have found rudimentary parts as useful as, or even sometimes more useful than, parts of high physiological importance. Rudimentary organs may be compared with the letters in a word, still retained in the spelling, but become useless in the pronunciation, but which serve as a clue in seeking for its derivation. On the view of descent with modification, we may conclude that the existence of organs in a rudimentary, imperfect, and useless condition, or quite aborted, far from presenting a strange difficulty, as they assuredly do on the ordinary doctrine of creation, might even have been anticipated, and can be accounted for by the laws of inheritance.

SUMMARY.

In this chapter I have attempted to show, that the subordination of group to group in all organisms throughout all time; that the nature of the relationship, by which all living and extinct beings are united by complex, radiating, and circuitous lines of affinities into one grand system; the rules followed and the difficulties encountered by naturalists in their classifications; the value set upon characters, if constant and prevalent, whether of high vital importance, or of the most trifling importance, or, as in rudimentary organs, of no importance; the wide opposition²²⁸ in value between analogical or adaptive characters, and characters of true affinity; and other such rules;--all naturally follow on the view of the common parentage of those forms which are considered by naturalists as allied, together with their modification through natural selection, with its contingencies of extinction and divergence of character. In considering this view of classification, it should be borne in mind that the element of descent has been universally used in ranking together the sexes, ages, and acknowledged varieties of the same species, however different they may be in structure. If we extend the use of this element of descent,--the only certainly known cause of similarity in organic beings,--we shall understand what is meant by the natural system: it is genealogical in its attempted arrangement, with the grades of acquired difference marked by the terms varieties, species, genera, families, orders, and classes.

On this same view of descent with modification, all the great facts in Morphology become intelligible,--whether we look to the same pattern displayed in the homologous organs, to whatever purpose applied²²⁹, of the different species of a class; or to the homologous parts constructed on the same pattern in each individual animal and plant.

On the principle of successive slight variations, not necessarily or generally supervening at a very early period of life, and being inherited at a corresponding period, we can understand the great leading facts in Embryology; namely, the resemblance in an individual embryo of the homologous parts, which when matured will become widely different from each other in structure and function; and the resemblance in different species of a class of the homologous parts or organs, though fitted in the adult members for purposes as different as possible. Larvae are active embryos, which have become specially modified in relation to their habits of life, through the principle of modifications being inherited at corresponding ages. On this same principle--and bearing in mind, that when organs are reduced in size, either from disuse or selection, it will generally be at that period of life when the being has to provide for its own wants, and bearing in mind how strong is the principle of inheritance--the occurrence of rudimentary organs and their final abortion, present to us no inexplicable difficulties; on the contrary, their presence might have been even anticipated. The importance of embryological characters and of rudimentary organs in classification is intelligible, on the view that an arrangement is only so far natural as it is genealogical.

Finally, the several classes of facts which have been considered in this chapter, seem to me to proclaim so plainly, that the innumerable species, genera, and families of organic beings, with which this world is peopled, have all descended, each within its own class or group, from common parents, and have all been modified in the course of descent, that I should without hesitation²³⁰ adopt this view, even if it were unsupported by other facts or arguments.

1 mutual   

adj.相互的，彼此的；共同的，共有的

参考例句：

• We must pull together for mutual interest.我们必须为相互的利益而通力合作。
• Mutual interests tied us together.相互的利害关系把我们联系在一起。

2 affinities   

n.密切关系( affinity的名词复数 )；亲近；（生性）喜爱；类同

参考例句：

• Cubism had affinities with the new European interest in Jazz. 主体派和欧洲新近的爵士音乐热有密切关系。 来自辞典例句
• The different isozymes bind calcium ions with different affinities. 不同的同功酶以不同的亲和力与钙离子相结合。 来自辞典例句

3 fin   

n.鳍；(飞机的)安定翼

参考例句：

• They swim using a small fin on their back.它们用背上的小鳍游动。
• The aircraft has a long tail fin.那架飞机有一个长长的尾翼。

4 embryo   

n.胚胎，萌芽的事物

参考例句：

• They are engaging in an embryo research.他们正在进行一项胚胎研究。
• The project was barely in embryo.该计划只是个雏形。

5 rudiment   

n.初步；初级；基本原理

参考例句：

• The rudiment with the capitalism,new developing citizens stratum appeared in the society in the ming dynasty.伴随着资本主义的萌芽，明代社会出现了新兴的市民阶层。
• It do not take me long to pick up the rudiment of the language.我没有费多少时间就学会了这一语言的初步知识。

6 modification   

n.修改，改进，缓和，减轻

参考例句：

• The law,in its present form,is unjust;it needs modification.现行的法律是不公正的，它需要修改。
• The design requires considerable modification.这个设计需要作大的修改。

7 extinction   

n.熄灭，消亡，消灭，灭绝，绝种

参考例句：

• The plant is now in danger of extinction.这种植物现在有绝种的危险。
• The island's way of life is doomed to extinction.这个岛上的生活方式注定要消失。

8 descending   

n. 下行 adj. 下降的

参考例句：

• The results are expressed in descending numerical order . 结果按数字降序列出。
• The climbers stopped to orient themselves before descending the mountain. 登山者先停下来确定所在的位置，然后再下山。

9 constellations   

n.星座( constellation的名词复数 )；一群杰出人物；一系列（相关的想法、事物）；一群（相关的人）

参考例句：

• The map of the heavens showed all the northern constellations. 这份天体图标明了北半部所有的星座。 来自《简明英汉词典》
• His time was coming, he would move in the constellations of power. 他时来运转，要进入权力中心了。 来自教父部分

10 diffused   

散布的，普及的，扩散的

参考例句：

• A drop of milk diffused in the water. 一滴牛奶在水中扩散开来。
• Gases and liquids diffused. 气体和液体慢慢混合了。

11 dominant   

adj.支配的，统治的；占优势的；显性的；n.主因，要素，主要的人(或物)；显性基因

参考例句：

• The British were formerly dominant in India.英国人从前统治印度。
• She was a dominant figure in the French film industry.她在法国电影界是个举足轻重的人物。

12 incipient   

adj.起初的，发端的，初期的

参考例句：

• The anxiety has been sharpened by the incipient mining boom.采矿业初期的蓬勃发展加剧了这种担忧。
• What we see then is an incipient global inflation.因此，我们看到的是初期阶段的全球通胀.

13 diverge   

v.分叉，分歧，离题，使...岔开，使转向

参考例句：

• This is where our opinions diverge from each other.这就是我们意见产生分歧之处。
• Don't diverge in your speech.发言不要离题。

14 diverging   

分开( diverge的现在分词 )； 偏离； 分歧； 分道扬镳

参考例句：

• Plants had gradually evolved along diverging and converging pathways. 植物是沿着趋异和趋同两种途径逐渐演化的。
• With member-country bond yields now diverging, 'it's a fragmented set of markets. 但随着成员国债券收益率之差扩大，市场已经分割开来。

15 supplant   

vt.排挤；取代

参考例句：

• Electric cars may one day supplant petrol-driven ones.也许有一天电动车会取代汽油驱动的车。
• The law of momentum conservation could supplant Newton's third law.动量守恒定律可以取代牛顿第三定律。

16 exterminate   

v.扑灭，消灭，根绝

参考例句：

• Some people exterminate garden insects by spraying poison on the plants.有些人在植物上喷撒毒剂以杀死花园内的昆虫。
• Woodpeckers can exterminate insect pests hiding in trees.啄木鸟能消灭躲在树里的害虫。

17 illustrating   

给…加插图( illustrate的现在分词 )； 说明； 表明； （用示例、图画等）说明

参考例句：

• He upstaged the other speakers by illustrating his talk with slides. 他演讲中配上幻灯片，比其他演讲人更吸引听众。
• Material illustrating detailed structure of graptolites has been etched from limestone by means of hydrofluoric acid. 表明笔石详细构造的物质是利用氢氟酸从石灰岩中侵蚀出来。

18 formerly   

adv.从前，以前

参考例句：

• We now enjoy these comforts of which formerly we had only heard.我们现在享受到了过去只是听说过的那些舒适条件。
• This boat was formerly used on the rivers of China.这船从前航行在中国内河里。

19 inevitable   

adj.不可避免的，必然发生的

参考例句：

• Mary was wearing her inevitable large hat.玛丽戴着她总是戴的那顶大帽子。
• The defeat had inevitable consequences for British policy.战败对英国政策不可避免地产生了影响。

20 proceeding   

n.行动，进行，(pl.)会议录，学报

参考例句：

• This train is now proceeding from Paris to London.这次列车从巴黎开往伦敦。
• The work is proceeding briskly.工作很有生气地进展着。

21 progenitor   

n.祖先，先驱

参考例句：

• He was also a progenitor of seven presidents of Nicaragua.他也是尼加拉瓜7任总统的祖先。
• Schoenberg was a progenitor of modern music.勋伯格是一位现代音乐的先驱。

22 descended   

a.为...后裔的，出身于...的

参考例句：

• A mood of melancholy descended on us. 一种悲伤的情绪袭上我们的心头。
• The path descended the hill in a series of zigzags. 小路呈连续的之字形顺着山坡蜿蜒而下。

23 diverged   

分开( diverge的过去式和过去分词 )； 偏离； 分歧； 分道扬镳

参考例句：

• Who knows when we'll meet again? 不知几时咱们能再见面！
• At what time do you get up? 你几时起床？

24 sufficiently   

adv.足够地，充分地

参考例句：

• It turned out he had not insured the house sufficiently.原来他没有给房屋投足保险。
• The new policy was sufficiently elastic to accommodate both views.新政策充分灵活地适用两种观点。

25 judgment   

n.审判；判断力，识别力，看法，意见

参考例句：

• The chairman flatters himself on his judgment of people.主席自认为他审视人比别人高明。
• He's a man of excellent judgment.他眼力过人。

26 fully   

adv.完全地，全部地，彻底地；充分地

参考例句：

• The doctor asked me to breathe in,then to breathe out fully.医生让我先吸气，然后全部呼出。
• They soon became fully integrated into the local community.他们很快就完全融入了当地人的圈子。

27 naturalist   

n.博物学家(尤指直接观察动植物者)

参考例句：

• He was a printer by trade and naturalist by avocation.他从事印刷业，同时是个博物学爱好者。
• The naturalist told us many stories about birds.博物学家给我们讲述了许多有关鸟儿的故事。

28 naturalists   

n.博物学家( naturalist的名词复数 )；（文学艺术的）自然主义者

参考例句：

• Naturalists differ much in determining what characters are of generic value. 自然学者对于不同性状决定生物的属的含义上，各有各的见解。 来自辞典例句
• This fact has led naturalists to believe that the Isthmus was formerly open. 使许多自然学者相信这个地蛱在以前原是开通的。 来自辞典例句

29 mere   

adj.纯粹的；仅仅，只不过

参考例句：

• That is a mere repetition of what you said before.那不过是重复了你以前讲的话。
• It's a mere waste of time waiting any longer.再等下去纯粹是浪费时间。

30 briefly   

adv.简单地，简短地

参考例句：

• I want to touch briefly on another aspect of the problem.我想简单地谈一下这个问题的另一方面。
• He was kidnapped and briefly detained by a terrorist group.他被一个恐怖组织绑架并短暂拘禁。

31 ingenuity   

n.别出心裁；善于发明创造

参考例句：

• The boy showed ingenuity in making toys.那个小男孩做玩具很有创造力。
• I admire your ingenuity and perseverance.我钦佩你的别出心裁和毅力。

32 specified   

adj.特定的

参考例句：

• The architect specified oak for the wood trim. 那位建筑师指定用橡木做木饰条。
• It is generated by some specified means. 这是由某些未加说明的方法产生的。

33 conceal   

v.隐藏，隐瞒，隐蔽

参考例句：

• He had to conceal his identity to escape the police.为了躲避警方，他只好隐瞒身份。
• He could hardly conceal his joy at his departure.他几乎掩饰不住临行时的喜悦。

34 concealed   

a.隐藏的，隐蔽的

参考例句：

• The paintings were concealed beneath a thick layer of plaster. 那些画被隐藏在厚厚的灰泥层下面。
• I think he had a gun concealed about his person. 我认为他当时身上藏有一支枪。

35 partially   

adv.部分地，从某些方面讲

参考例句：

• The door was partially concealed by the drapes.门有一部分被门帘遮住了。
• The police managed to restore calm and the curfew was partially lifted.警方设法恢复了平静，宵禁部分解除。

36 determined   

adj.坚定的；有决心的

参考例句：

• I have determined on going to Tibet after graduation.我已决定毕业后去西藏。
• He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。

37 recur   

vi.复发，重现，再发生

参考例句：

• Economic crises recur periodically.经济危机周期性地发生。
• Of course,many problems recur at various periods.当然，有许多问题会在不同的时期反复提出。

38 organisation   

n.组织，安排，团体，有机休

参考例句：

• The method of his organisation work is worth commending.他的组织工作的方法值得称道。
• His application for membership of the organisation was rejected.他想要加入该组织的申请遭到了拒绝。

39 modifications   

n.缓和( modification的名词复数 )；限制；更改；改变

参考例句：

• The engine was pulled apart for modifications and then reassembled. 发动机被拆开改型，然后再组装起来。 来自《简明英汉词典》
• The original plan had undergone fairly extensive modifications. 原计划已经作了相当大的修改。 来自《简明英汉词典》

40 remarkable   

adj.显著的，异常的，非凡的，值得注意的

参考例句：

• She has made remarkable headway in her writing skills.她在写作技巧方面有了长足进步。
• These cars are remarkable for the quietness of their engines.这些汽车因发动机没有噪音而不同凡响。

41 paramount   

a.最重要的，最高权力的

参考例句：

• My paramount object is to save the Union and destroy slavery.我的最高目标是拯救美国，摧毁奴隶制度。
• Nitrogen is of paramount importance to life on earth.氮对地球上的生命至关重要。

42 physiological   

adj.生理学的，生理学上的

参考例句：

• He bought a physiological book.他买了一本生理学方面的书。
• Every individual has a physiological requirement for each nutrient.每个人对每种营养成分都有一种生理上的需要。

43 allied   

adj.协约国的；同盟国的

参考例句：

• Britain was allied with the United States many times in history.历史上英国曾多次与美国结盟。
• Allied forces sustained heavy losses in the first few weeks of the campaign.同盟国在最初几周内遭受了巨大的损失。

44 generic   

adj.一般的，普通的，共有的

参考例句：

• I usually buy generic clothes instead of name brands.我通常买普通的衣服，不买名牌。
• The generic woman appears to have an extraordinary faculty for swallowing the individual.一般妇女在婚后似乎有特别突出的抑制个性的能力。

45 apprehend   

vt.理解，领悟，逮捕，拘捕，忧虑

参考例句：

• I apprehend no worsening of the situation.我不担心局势会恶化。
• Police have not apprehended her killer.警察还未抓获谋杀她的凶手。

46 entirely   

ad.全部地，完整地；完全地，彻底地

参考例句：

• The fire was entirely caused by their neglect of duty. 那场火灾完全是由于他们失职而引起的。
• His life was entirely given up to the educational work. 他的一生统统献给了教育工作。

47 insufficient   

adj.(for，of)不足的，不够的

参考例句：

• There was insufficient evidence to convict him.没有足够证据给他定罪。
• In their day scientific knowledge was insufficient to settle the matter.在他们的时代，科学知识还不能足以解决这些问题。

48 antennae   

n.天线；触角

参考例句：

• Sometimes a creature uses a pair of antennae to swim.有时某些动物使用其一对触须来游泳。
• Cuba's government said that Cubans found watching American television on clandestine antennae would face three years in jail.古巴政府说那些用秘密天线收看美国电视的古巴人将面临三年监禁。

49 atrophied   

adj.萎缩的，衰退的v.（使）萎缩，（使）虚脱，（使）衰退( atrophy的过去式和过去分词 )

参考例句：

• Patients exercised their atrophied limbs in the swimming pool. 病人们在泳池里锻炼萎缩的四肢。 来自辞典例句
• Method: Using microwave tissue thermocoaqulation to make chronic tonsillitis coagulated and atrophied. 方法：采用微波热凝方法使慢性扁桃体炎组织凝固、萎缩。 来自互联网

50 undoubtedly   

adv.确实地，无疑地

参考例句：

• It is undoubtedly she who has said that.这话明明是她说的。
• He is undoubtedly the pride of China.毫无疑问他是中国的骄傲。

51 jaw   

n.颚，颌，说教，流言蜚语；v.喋喋不休，教训

参考例句：

• He delivered a right hook to his opponent's jaw.他给了对方下巴一记右钩拳。
• A strong square jaw is a sign of firm character.强健的方下巴是刚毅性格的标志。

52 jaws   

n.口部；嘴

参考例句：

• The antelope could not escape the crocodile's gaping jaws. 那只羚羊无法从鱷鱼张开的大口中逃脱。
• The scored jaws of a vise help it bite the work. 台钳上有刻痕的虎钳牙帮助它紧咬住工件。

53 affinity   

n.亲和力，密切关系

参考例句：

• I felt a great affinity with the people of the Highlands.我被苏格兰高地人民深深地吸引。
• It's important that you share an affinity with your husband.和丈夫有共同的爱好是十分重要的。

54 derived   

vi.起源；由来；衍生；导出v.得到( derive的过去式和过去分词 )；（从…中）得到获得；源于；（从…中）提取

参考例句：

• Many English words are derived from Latin and Greek. 英语很多词源出于拉丁文和希腊文。 来自《简明英汉词典》
• He derived his enthusiasm for literature from his father. 他对文学的爱好是受他父亲的影响。 来自《简明英汉词典》

55 trifling   

adj.微不足道的；没什么价值的

参考例句：

• They quarreled over a trifling matter.他们为这种微不足道的事情争吵。
• So far Europe has no doubt, gained a real conveniency,though surely a very trifling one.直到现在为止,欧洲无疑地已经获得了实在的便利，不过那确是一种微不足道的便利。

56 nostril   

n.鼻孔

参考例句：

• The Indian princess wore a diamond in her right nostril.印弟安公主在右鼻孔中戴了一颗钻石。
• All South American monkeys have flat noses with widely spaced nostril.所有南美洲的猴子都有平鼻子和宽大的鼻孔。

57 nostrils   

鼻孔( nostril的名词复数 )

参考例句：

• Her nostrils flared with anger. 她气得两个鼻孔都鼓了起来。
• The horse dilated its nostrils. 马张大鼻孔。

58 reptiles   

n.爬行动物，爬虫( reptile的名词复数 )

参考例句：

• Snakes and crocodiles are both reptiles. 蛇和鳄鱼都是爬行动物。 来自《简明英汉词典》
• Birds, reptiles and insects come from eggs. 鸟类、爬虫及昆虫是卵生的。 来自《现代汉英综合大词典》

59 reptile   

n.爬行动物；两栖动物

参考例句：

• The frog is not a true reptile.青蛙并非真正的爬行动物。
• So you should not be surprised to see someone keep a reptile as a pet.所以，你不必惊奇有人养了一只爬行动物作为宠物。

60 marsupial   

adj.有袋的，袋状的

参考例句：

• Koala is an arboreal Australian marsupial.考拉是一种澳大利亚树栖有袋动物。
• The marsupial has been in decline for decades due to urban sprawl from car accidentsdog attacks.这种有袋动物其数量在过去几十年间逐渐减少,主要原因是城市的扩张、车祸和狗的袭击。

61 dermal   

adj.皮肤的，真皮的

参考例句：

• Dermal hypersensitivity usually does not develop until three to four weeks after onset. 皮肤过敏通常在起病后三、四周内不会出现。 来自辞典例句
• The doctor said permanent dermal pigmentation is a form of microsurgery. 医生说永久的皮肤染色是一种显微手术。 来自互联网

62 aggregate   

adj.总计的，集合的；n.总数；v.合计；集合

参考例句：

• The football team had a low goal aggregate last season.这支足球队上个赛季的进球总数很少。
• The money collected will aggregate a thousand dollars.进帐总额将达一千美元。

63 appreciation   

n.评价；欣赏；感谢；领会，理解；价格上涨

参考例句：

• I would like to express my appreciation and thanks to you all.我想对你们所有人表达我的感激和谢意。
• I'll be sending them a donation in appreciation of their help.我将送给他们一笔捐款以感谢他们的帮助。

64 illustrate   

v.举例说明，阐明；图解，加插图

参考例句：

• The company's bank statements illustrate its success.这家公司的银行报表说明了它的成功。
• This diagram will illustrate what I mean.这个图表可说明我的意思。

65 allocating   

分配，分派( allocate的现在分词 )； 把…拨给

参考例句：

• Administrative practice generally follows the judicial model in allocating burdens of proof. 在分配举证责任方面，行政实践通常遵循司法模式。
• A cyclical multiplexing technique, allocating resources in fixed-time slices. 以固定的时间片分配资源的循环复用技术。

66 lesser   

adj.次要的，较小的；adv.较小地，较少地

参考例句：

• Kept some of the lesser players out.不让那些次要的球员参加联赛。
• She has also been affected,but to a lesser degree.她也受到波及，但程度较轻。

67 botanist   

n.植物学家

参考例句：

• The botanist introduced a new species of plant to the region.那位植物学家向该地区引入了一种新植物。
• I had never talked with a botanist before,and I found him fascinating.我从没有接触过植物学那一类的学者，我觉得他说话极有吸引力。

68 aerating   

v.使暴露于空气中，使充满气体( aerate的现在分词 )

参考例句：

• Earthworms do the important job of aerating the soil. 蚯蚓做了使土壤透气的重要工作。
• First, heels are excellent for aerating lawns. 首先，高跟鞋用来给草坪通气是极好的。 来自互联网

69 embryonic   

adj.胚胎的

参考例句：

• It is still in an embryonic stage.它还处于萌芽阶段。
• The plan,as yet,only exists in embryonic form.这个计划迄今为止还只是在酝酿之中。

70 doctrine   

n.教义；主义；学说

参考例句：

• He was impelled to proclaim his doctrine.他不得不宣扬他的教义。
• The council met to consider changes to doctrine.宗教议会开会考虑更改教义。

71 crustacean   

n.甲壳动物；adj.甲壳纲的

参考例句：

• Seafood is a valuable lobster crustacean section.名贵海珍品龙虾属甲壳科。
• The illustrious Cuvier did not perceive that a barnacle was a crustacean.大名鼎鼎的居维叶也未看出藤壶是一种甲壳动物。

72 crustaceans   

n.甲壳纲动物（如蟹、龙虾）( crustacean的名词复数 )

参考例句：

• These crustaceans provide a valuable food source for some fish. 这些甲壳纲动物是某些鱼类重要的食物来源。 来自《简明英汉词典》
• When the tide ebbs it's a rock pool inhabited by crustaceans. 退潮时，它便成为甲壳动物居住的岩石区潮水潭。 来自辞典例句

73 geographical   

adj.地理的；地区(性)的

参考例句：

• The current survey will have a wider geographical spread.当前的调查将在更广泛的地域范围內进行。
• These birds have a wide geographical distribution.这些鸟的地理分布很广。

74 specially   

adv.特定地；特殊地；明确地

参考例句：

• They are specially packaged so that they stack easily.它们经过特别包装以便于堆放。
• The machine was designed specially for demolishing old buildings.这种机器是专为拆毁旧楼房而设计的。

75 botanists   

n.植物学家，研究植物的人( botanist的名词复数 )

参考例句：

• Botanists had some difficulty categorizing the newly found plant. 植物学家们不大容易确定这种新发现的植物的种类。 来自辞典例句
• Botanists refer this flower to the rose family. 植物学家将这花归入蔷薇科。 来自辞典例句

76 structural   

adj.构造的，组织的，建筑（用）的

参考例句：

• The storm caused no structural damage.风暴没有造成建筑结构方面的破坏。
• The North American continent is made up of three great structural entities.北美大陆是由三个构造单元组成的。

77 unity   

n.团结，联合，统一；和睦，协调

参考例句：

• When we speak of unity,we do not mean unprincipled peace.所谓团结，并非一团和气。
• We must strengthen our unity in the face of powerful enemies.大敌当前，我们必须加强团结。

78 enunciation   

n.清晰的发音；表明，宣言；口齿

参考例句：

• He is always willing to enunciate his opinions on the subject of politics. 他总是愿意对政治问题发表意见。> enunciation / I9nQnsI5eIFn; I9nQnsI`eFEn/ n [C, U]。 来自辞典例句
• Be good at communicating,sense of responsibility,the work is careful,the enunciation is clear. 善于沟通，责任心强，工作细致，口齿清晰。 来自互联网

79 strictly   

adv.严厉地，严格地；严密地

参考例句：

• His doctor is dieting him strictly.他的医生严格规定他的饮食。
• The guests were seated strictly in order of precedence.客人严格按照地位高低就座。

80 err   

vi.犯错误，出差错

参考例句：

• He did not err by a hair's breadth in his calculation.他的计算结果一丝不差。
• The arrows err not from their aim.箭无虚发。

81 epoch   

n.(新)时代；历元

参考例句：

• The epoch of revolution creates great figures.革命时代造就伟大的人物。
• We're at the end of the historical epoch,and at the dawn of another.我们正处在一个历史时代的末期，另一个历史时代的开端。

82 anterior   

adj.较早的；在前的

参考例句：

• We've already finished the work anterior to the schedule.我们已经提前完成了工作。
• The anterior part of a fish contains the head and gills.鱼的前部包括头和鳃。

83 metaphorically   

adv. 用比喻地

参考例句：

• It is context and convention that determine whether a term will be interpreted literally or metaphorically. 对一个词的理解是按字面意思还是隐喻的意思要视乎上下文和习惯。
• Metaphorically it implied a sort of admirable energy. 从比喻来讲，它含有一种令人赞许的能量的意思。

84 metaphorical   

a.隐喻的，比喻的

参考例句：

• Here, then, we have a metaphorical substitution on a metonymic axis. 这样，我们在换喻（者翻译为转喻，一种以部分代替整体的修辞方法）上就有了一个隐喻的替代。
• So, in a metaphorical sense, entropy is arrow of time. 所以说，我们可以这样作个比喻：熵像是时间之矢。

85 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

86 isolated   

adj.与世隔绝的

参考例句：

• His bad behaviour was just an isolated incident. 他的不良行为只是个别事件。
• Patients with the disease should be isolated. 这种病的患者应予以隔离。

87 possessed   

adj.疯狂的；拥有的，占有的

参考例句：

• He flew out of the room like a man possessed.他像着了魔似地猛然冲出房门。
• He behaved like someone possessed.他行为举止像是魔怔了。

88 isolation   

n.隔离，孤立，分解，分离

参考例句：

• The millionaire lived in complete isolation from the outside world.这位富翁过着与世隔绝的生活。
• He retired and lived in relative isolation.他退休后，生活比较孤寂。

89 civilisation   

n.文明，文化，开化，教化

参考例句：

• Energy and ideas are the twin bases of our civilisation.能源和思想是我们文明的两大基石。
• This opera is one of the cultural totems of Western civilisation.这部歌剧是西方文明的文化标志物之一。

90 confirmation   

n.证实，确认，批准

参考例句：

• We are waiting for confirmation of the news.我们正在等待证实那个消息。
• We need confirmation in writing before we can send your order out.给你们发送订购的货物之前，我们需要书面确认。

91 requisite   

adj.需要的，必不可少的；n.必需品

参考例句：

• He hasn't got the requisite qualifications for the job.他不具备这工作所需的资格。
• Food and air are requisite for life.食物和空气是生命的必需品。

92 turnips   

芜青( turnip的名词复数 )； 芜菁块根； 芜菁甘蓝块根； 怀表

参考例句：

• Well, I like turnips, tomatoes, eggplants, cauliflowers, onions and carrots. 噢，我喜欢大萝卜、西红柿、茄子、菜花、洋葱和胡萝卜。 来自魔法英语-口语突破（高中）
• This is turnip soup, made from real turnips. 这是大头菜汤，用真正的大头菜做的。

93 turnip   

n.萝卜，芜菁

参考例句：

• The turnip provides nutrition for you.芜菁为你提供营养。
• A turnip is a root vegetable.芜菁是根茎类植物。

94 beak   

n.鸟嘴，茶壶嘴，钩形鼻

参考例句：

• The bird had a worm in its beak.鸟儿嘴里叼着一条虫。
• This bird employs its beak as a weapon.这种鸟用嘴作武器。

95 solely   

adv.仅仅，唯一地

参考例句：

• Success should not be measured solely by educational achievement.成功与否不应只用学业成绩来衡量。
• The town depends almost solely on the tourist trade.这座城市几乎完全靠旅游业维持。

96 primrose   

n.樱草，最佳部分，

参考例句：

• She is in the primrose of her life.她正处在她一生的最盛期。
• The primrose is set off by its nest of green.一窝绿叶衬托着一朵樱草花。

97 previously   

adv.以前，先前（地）

参考例句：

• The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
• Let me digress for a moment and explain what had happened previously.让我岔开一会儿，解释原先发生了什么。

98 spike   

n.长钉，钉鞋；v.以大钉钉牢，使...失效

参考例句：

• The spike pierced the receipts and held them in order.那个钉子穿过那些收据并使之按顺序排列。
• They'll do anything to spike the guns of the opposition.他们会使出各种手段来挫败对手。

99 immediate   

adj.立即的；直接的，最接近的；紧靠的

参考例句：

• His immediate neighbours felt it their duty to call.他的近邻认为他们有责任去拜访。
• We declared ourselves for the immediate convocation of the meeting.我们主张立即召开这个会议。

100 preposterous   

adj.荒谬的，可笑的

参考例句：

• The whole idea was preposterous.整个想法都荒唐透顶。
• It would be preposterous to shovel coal with a teaspoon.用茶匙铲煤是荒谬的。

101 larvae   

n.幼虫

参考例句：

• Larvae are parasitic on sheep.幼虫寄生在绵羊的身上。
• The larvae prey upon small aphids.这种幼虫以小蚜虫为食。

102 systematist   

n.组织主义者

参考例句：

103 aggregated   

a.聚合的，合计的

参考例句：

• He aggregated her to a political party. 他吸收她参加一政党。
• The audiences aggregated a million people. 观众总数达100万人。

104 moth   

n.蛾，蛀虫

参考例句：

• A moth was fluttering round the lamp.有一只蛾子扑打着翅膀绕着灯飞。
• The sweater is moth-eaten.毛衣让蛀虫咬坏了。

105 drawn   

v.拖，拉，拔出；adj.憔悴的，紧张的

参考例句：

• All the characters in the story are drawn from life.故事中的所有人物都取材于生活。
• Her gaze was drawn irresistibly to the scene outside.她的目光禁不住被外面的风景所吸引。

106 paradox   

n.似乎矛盾却正确的说法；自相矛盾的人(物)

参考例句：

• The story contains many levels of paradox.这个故事存在多重悖论。
• The paradox is that Japan does need serious education reform.矛盾的地方是日本确实需要教育改革。

107 aberrant   

adj.畸变的，异常的，脱离常轨的

参考例句：

• His aberrant behavior at the party shocked everyone.他在晚会上的异常举止令所有人感到震惊！
• I saw that the insects and spiders were displaying the same kind of aberrant behavior.我看到昆虫和蜘蛛正在表现出相同反常的行为。

108 exterminated   

v.消灭，根绝( exterminate的过去式和过去分词 )

参考例句：

• It was exterminated root and branch. 它被彻底剪除了。 来自《现代汉英综合大词典》
• The insects can be exterminated by spraying DDT. 可以用喷撒滴滴涕的方法大量杀死这种昆虫。 来自《用法词典》

109 utterly   

adv.完全地，绝对地

参考例句：

• Utterly devoted to the people,he gave his life in saving his patients.他忠于人民，把毕生精力用于挽救患者的生命。
• I was utterly ravished by the way she smiled.她的微笑使我完全陶醉了。

110 severely   

adv.严格地；严厉地；非常恶劣地

参考例句：

• He was severely criticized and removed from his post.他受到了严厉的批评并且被撤了职。
• He is severely put down for his careless work.他因工作上的粗心大意而受到了严厉的批评。

111 investigation   

n.调查，调查研究

参考例句：

• In an investigation,a new fact became known, which told against him.在调查中新发现了一件对他不利的事实。
• He drew the conclusion by building on his own investigation.他根据自己的调查研究作出结论。

112 favourable   

adj.赞成的，称赞的，有利的，良好的，顺利的

参考例句：

• The company will lend you money on very favourable terms.这家公司将以非常优惠的条件借钱给你。
• We found that most people are favourable to the idea.我们发现大多数人同意这个意见。

113 rodents   

n.啮齿目动物( rodent的名词复数 )

参考例句：

• Rodents carry diseases and are generally regarded as pests. 啮齿目动物传播疾病，常被当作害虫对待。 来自《简明英汉词典》
• Some wild rodents in Africa also harbor the virus. 在非洲，有些野生啮齿动物也是储毒者。 来自辞典例句

114 rodent   

n.啮齿动物；adj.啮齿目的

参考例句：

• When there is a full moon,this nocturnal rodent is careful to stay in its burrow.月圆之夜，这种夜间活动的啮齿类动物会小心地呆在地洞里不出来。
• This small rodent can scoop out a long,narrow tunnel in a very short time.这种小啮齿动物能在很短的时间里挖出一条又长又窄的地道来。

115 indirectly   

adv.间接地，不直接了当地

参考例句：

• I heard the news indirectly.这消息我是间接听来的。
• They were approached indirectly through an intermediary.通过一位中间人，他们进行了间接接触。

116 multiplication   

n.增加，增多，倍增；增殖，繁殖；乘法

参考例句：

• Our teacher used to drum our multiplication tables into us.我们老师过去老是让我们反覆背诵乘法表。
• The multiplication of numbers has made our club building too small.会员的增加使得我们的俱乐部拥挤不堪。

117 divergence   

n.分歧，岔开

参考例句：

• There is no sure cure for this transatlantic divergence.没有什么灵丹妙药可以消除大西洋两岸的分歧。
• In short,it was an age full of conflicts and divergence of values.总之，这一时期是矛盾与价值观分歧的时期。

118 retention   

n.保留，保持，保持力，记忆力

参考例句：

• They advocate the retention of our nuclear power plants.他们主张保留我们的核电厂。
• His retention of energy at this hour is really surprising.人们惊叹他在这个时候还能保持如此旺盛的精力。

119 circuitous   

adj.迂回的路的，迂曲的，绕行的

参考例句：

• They took a circuitous route to avoid reporters.他们绕道避开了记者。
• The explanation was circuitous and puzzling.这个解释很迂曲，让人困惑不解。

120 predecessors   

n.前任( predecessor的名词复数 )；前辈；（被取代的）原有事物；前身

参考例句：

• The new government set about dismantling their predecessors' legislation. 新政府正着手废除其前任所制定的法律。 来自《简明英汉词典》
• Will new plan be any more acceptable than its predecessors? 新计划比原先的计划更能令人满意吗？ 来自《简明英汉词典》

121 intervals   

n.[军事]间隔( interval的名词复数 )；间隔时间；[数学]区间；（戏剧、电影或音乐会的）幕间休息

参考例句：

• The forecast said there would be sunny intervals and showers. 预报间晴，有阵雨。
• Meetings take place at fortnightly intervals. 每两周开一次会。

122 progenitors   

n.祖先( progenitor的名词复数 )；先驱；前辈；原本

参考例句：

• The researchers also showed that the progenitors mature into neurons in Petri dishes. 研究人员还表示，在佩特里培养皿中的脑细胞前体可以发育成神经元。 来自英汉非文学 - 生命科学 - 大脑与疾病
• Though I am poor and wretched now, my progenitors were famously wealthy. 别看我现在穷困潦倒，我家上世可是有名的富翁。 来自互联网

123 distinguished   

adj.卓越的，杰出的，著名的

参考例句：

• Elephants are distinguished from other animals by their long noses.大象以其长长的鼻子显示出与其他动物的不同。
• A banquet was given in honor of the distinguished guests.宴会是为了向贵宾们致敬而举行的。

124 primordial   

adj.原始的；最初的

参考例句：

• It is the primordial force that propels us forward.它是推动我们前进的原始动力。
• The Neanderthal Man is one of our primordial ancestors.的尼安德特人是我们的原始祖先之一.

125 specify   

vt.指定，详细说明

参考例句：

• We should specify a time and a place for the meeting.我们应指定会议的时间和地点。
• Please specify what you will do.请你详述一下你将做什么。

126 inevitably   

adv.不可避免地；必然发生地

参考例句：

• In the way you go on,you are inevitably coming apart.照你们这样下去，毫无疑问是会散伙的。
• Technological changes will inevitably lead to unemployment.技术变革必然会导致失业。

127 mole   

n.胎块；痣；克分子

参考例句：

• She had a tiny mole on her cheek.她的面颊上有一颗小黑痣。
• The young girl felt very self- conscious about the large mole on her chin.那位年轻姑娘对自己下巴上的一颗大痣感到很不自在。

128 porpoise   

n.鼠海豚

参考例句：

• What is the difference between a dolphin and porpoise?海豚和和鼠海豚有什么区别？
• Mexico strives to save endangered porpoise.墨西哥努力拯救濒危的鼠海豚。

129 thigh   

n.大腿；股骨

参考例句：

• He is suffering from a strained thigh muscle.他的大腿肌肉拉伤了，疼得很。
• The thigh bone is connected to the hip bone.股骨连着髋骨。

130 proboscis   

n.（象的）长鼻

参考例句：

• Its proboscis has got stuck to a lot of pollen.它的喙上粘了很多花粉。
• It hovers in front of the flower,using its proboscis to look for nectar. 它在兰花前面飞来飞去, 用喙寻找花蜜.

131 bug   

n.虫子；故障；窃听器；vt.纠缠；装窃听器

参考例句：

• There is a bug in the system.系统出了故障。
• The bird caught a bug on the fly.那鸟在飞行中捉住了一只昆虫。

132 beetle   

n.甲虫，近视眼的人

参考例句：

• A firefly is a type of beetle.萤火虫是一种甲虫。
• He saw a shiny green beetle on a leaf.我看见树叶上有一只闪闪发光的绿色甲虫。

133 infinitely   

adv.无限地，无穷地

参考例句：

• There is an infinitely bright future ahead of us.我们有无限光明的前途。
• The universe is infinitely large.宇宙是无限大的。

134 analogous   

adj.相似的；类似的

参考例句：

• The two situations are roughly analogous.两种情況大致相似。
• The company is in a position closely analogous to that of its main rival.该公司与主要竞争对手的处境极为相似。

135 correlation   

n.相互关系，相关，关连

参考例句：

• The second group of measurements had a high correlation with the first.第二组测量数据与第一组高度相关。
• A high correlation exists in America between education and economic position.教育和经济地位在美国有极密切的关系。

136 enveloped   

v.包围，笼罩，包住( envelop的过去式和过去分词 )

参考例句：

• She was enveloped in a huge white towel. 她裹在一条白色大毛巾里。
• Smoke from the burning house enveloped the whole street. 燃烧着的房子冒出的浓烟笼罩了整条街。 来自《简明英汉词典》

137 membrane   

n.薄膜，膜皮，羊皮纸

参考例句：

• A vibrating membrane in the ear helps to convey sounds to the brain.耳膜的振动帮助声音传送到大脑。
• A plastic membrane serves as selective diffusion barrier.一层塑料薄膜起着选择性渗透屏障的作用。

138 lengthened   

（时间或空间）延长，伸长( lengthen的过去式和过去分词 )

参考例句：

• The afternoon shadows lengthened. 下午影子渐渐变长了。
• He wanted to have his coat lengthened a bit. 他要把上衣放长一些。

139 atrophy   

n./v.萎缩，虚脱，衰退

参考例句：

• Patients exercised their atrophied limbs in the swimming pool.病人们在泳池里锻炼萎缩的四肢。
• Many hoped he would renew the country's atrophied political system.很多人都期望他能使该国萎靡的政治体系振作起来。

140 abortion   

n.流产，堕胎

参考例句：

• She had an abortion at the women's health clinic.她在妇女保健医院做了流产手术。
• A number of considerations have led her to have a wilful abortion.多种考虑使她执意堕胎。

141 soldering   

n.软焊；锡焊；低温焊接；热焊接v.（使）焊接，焊合( solder的现在分词 )

参考例句：

• Care must be exercised in attaching the lead wires to the soldering tabs. 在往接线片上焊导线时必须非常小心。 来自辞典例句
• I suggest posing me with a soldering wand over my head like a sword. 我想让自己这样像把剑一样把电焊杆举过头顶。 来自电影对白

142 physiologist   

n.生理学家

参考例句：

• Russian physiologist who observed conditioned salivary responses in dogs (1849-1936). （1849-1936）苏联生理学家，在狗身上观察到唾液条件反射，曾获1904年诺贝尔生理学-医学奖。
• The physiologist recently studied indicated that evening exercises beneficially. 生理学家新近研究表明，傍晚锻炼最为有益。

143 physiologists   

n.生理学者( physiologist的名词复数 )；生理学( physiology的名词复数 )；生理机能

参考例句：

• Quite unexpectedly, vertebrate physiologists and microbial biochemists had found a common ground. 出乎意外，脊椎动物生理学家和微生物生化学家找到了共同阵地。 来自辞典例句
• Physiologists are interested in the workings of the human body. 生理学家对人体的功能感兴趣。 来自辞典例句

144 skull   

n.头骨；颅骨

参考例句：

• The skull bones fuse between the ages of fifteen and twenty-five.头骨在15至25岁之间长合。
• He fell out of the window and cracked his skull.他从窗子摔了出去，跌裂了颅骨。

145 petals   

n.花瓣( petal的名词复数 )

参考例句：

• white petals tinged with blue 略带蓝色的白花瓣
• The petals of many flowers expand in the sunshine. 许多花瓣在阳光下开放。 来自《现代英汉综合大词典》

146 intelligible   

adj.可理解的，明白易懂的，清楚的

参考例句：

• This report would be intelligible only to an expert in computing.只有计算机运算专家才能看懂这份报告。
• His argument was barely intelligible.他的论点不易理解。

147 spire   

n.(教堂)尖顶，尖塔，高点

参考例句：

• The church spire was struck by lightning.教堂的尖顶遭到了雷击。
• They could just make out the spire of the church in the distance.他们只能辨认出远处教堂的尖塔。

148 monstrous   

adj.巨大的；恐怖的；可耻的，丢脸的

参考例句：

• The smoke began to whirl and grew into a monstrous column.浓烟开始盘旋上升，形成了一个巨大的烟柱。
• Your behaviour in class is monstrous!你在课堂上的行为真是丢人！

149 inexplicable   

adj.无法解释的，难理解的

参考例句：

• It is now inexplicable how that development was misinterpreted.当时对这一事态发展的错误理解究竟是怎么产生的，现在已经无法说清楚了。
• There are many things which are inexplicable by science.有很多事科学还无法解释。

150 extraordinarily   

adv.格外地；极端地

参考例句：

• She is an extraordinarily beautiful girl.她是个美丽非凡的姑娘。
• The sea was extraordinarily calm that morning.那天清晨，大海出奇地宁静。

151 parturition   

n.生产，分娩

参考例句：

• Did the parturition go well yesterday evening?昨天晚上分娩顺利吗？
• She is a well-known parturition hastening midwife.她是这一带有名的催生婆。

152 skulls   

颅骨( skull的名词复数 )； 脑袋； 脑子； 脑瓜

参考例句：

• One of the women's skulls found exceeds in capacity that of the average man of today. 现已发现的女性颅骨中，其中有一个的脑容量超过了今天的普通男子。
• We could make a whole plain white with skulls in the moonlight! 我们便能令月光下的平原变白，遍布白色的骷髅！

153 appendage   

n.附加物

参考例句：

• After their work,the calculus was no longer an appendage and extension of Greek geometry.经过他们的工作，微积分不再是古希腊几何的附庸和延展。
• Macmillan must have loathed being judged as a mere appendage to domestic politics.麦克米伦肯定极不喜欢只被当成国内政治的附属品。

154 appendages   

n.附属物( appendage的名词复数 )；依附的人；附属器官；附属肢体（如臂、腿、尾等）

参考例句：

• The 11th segment carries a pair of segmented appendages, the cerci. 第十一节有一对分节的附肢，即尾须。 来自辞典例句
• Paired appendages, with one on each side of the body, are common in many animals. 很多动物身上有成对的附肢，一侧一个，这是很普遍的现象。 来自辞典例句

155 eminent   

adj.显赫的，杰出的，有名的，优良的

参考例句：

• We are expecting the arrival of an eminent scientist.我们正期待一位著名科学家的来访。
• He is an eminent citizen of China.他是一个杰出的中国公民。

156 eminently   

adv.突出地；显著地；不寻常地

参考例句：

• She seems eminently suitable for the job. 她看来非常适合这个工作。
• It was an eminently respectable boarding school. 这是所非常好的寄宿学校。 来自《简明英汉词典》

157 primordially   

adv.原始地，最初地

参考例句：

158 serial   

n.连本影片，连本电视节目；adj.连续的

参考例句：

• A new serial is starting on television tonight.今晚电视开播一部新的电视连续剧。
• Can you account for the serial failures in our experiment?你能解释我们实验屡屡失败的原因吗？

159 crab   

n.螃蟹，偏航，脾气乖戾的人，酸苹果；vi.捕蟹，偏航，发牢骚；vt.使偏航，发脾气

参考例句：

• I can't remember when I last had crab.我不记得上次吃蟹是什么时候了。
• The skin on my face felt as hard as a crab's back.我脸上的皮仿佛僵硬了，就象螃蟹的壳似的。

160 crabs   

n.蟹( crab的名词复数 )；阴虱寄生病；蟹肉v.捕蟹( crab的第三人称单数 )

参考例句：

• As we walked along the seashore we saw lots of tiny crabs. 我们在海岸上散步时看到很多小蟹。 来自《简明英汉词典》
• The fish and crabs scavenge for decaying tissue. 鱼和蟹搜寻腐烂的组织为食。 来自《简明英汉词典》

161 literally   

adv.照字面意义，逐字地；确实

参考例句：

• He translated the passage literally.他逐字逐句地翻译这段文字。
• Sometimes she would not sit down till she was literally faint.有时候，她不走到真正要昏厥了，决不肯坐下来。

162 casually   

adv.漠不关心地，无动于衷地，不负责任地

参考例句：

• She remarked casually that she was changing her job.她当时漫不经心地说要换工作。
• I casually mentioned that I might be interested in working abroad.我不经意地提到我可能会对出国工作感兴趣。

163 embryos   

n.晶胚；胚，胚胎( embryo的名词复数 )

参考例句：

• Somatic cells of angiosperms enter a regenerative phase and behave like embryos. 被子植物体细胞进入一个生殖阶段，而且其行为象胚。 来自辞典例句
• Evolution can explain why human embryos look like gilled fishes. 进化论能够解释为什么人类的胚胎看起来象除去了内脏的鱼一样。 来自辞典例句

164 moths   

n.蛾( moth的名词复数 )

参考例句：

• The moths have eaten holes in my wool coat. 蛀虫将我的羊毛衫蛀蚀了几个小洞。 来自《简明英汉词典》
• The moths tapped and blurred at the window screen. 飞蛾在窗帘上跳来跳去，弄上了许多污点。 来自《现代英汉综合大词典》

165 beetles   

n.甲虫( beetle的名词复数 )

参考例句：

• Beetles bury pellets of dung and lay their eggs within them. 甲壳虫把粪粒埋起来，然后在里面产卵。 来自《简明英汉词典》
• This kind of beetles have hard shell. 这类甲虫有坚硬的外壳。 来自《现代汉英综合大词典》

166 spotted   

adj.有斑点的，斑纹的，弄污了的

参考例句：

• The milkman selected the spotted cows,from among a herd of two hundred.牛奶商从一群200头牛中选出有斑点的牛。
• Sam's shop stocks short spotted socks.山姆的商店屯积了有斑点的短袜。

167 peculiar   

adj.古怪的，异常的；特殊的，特有的

参考例句：

• He walks in a peculiar fashion.他走路的样子很奇特。
• He looked at me with a very peculiar expression.他用一种很奇怪的表情看着我。

168 arteries   

n.动脉( artery的名词复数 )；干线，要道

参考例句：

• Even grafting new blood vessels in place of the diseased coronary arteries has been tried. 甚至移植新血管代替不健康的冠状动脉的方法都已经试过。 来自《简明英汉词典》
• This is the place where the three main arteries of West London traffic met. 这就是伦敦西部三条主要交通干线的交汇处。 来自《简明英汉词典》

169 slits   

n.狭长的口子，裂缝( slit的名词复数 )v.切开，撕开( slit的第三人称单数 )；在…上开狭长口子

参考例句：

• He appears to have two slits for eyes. 他眯着两眼。
• "You go to--Halifax,'she said tensely, her green eyes slits of rage. "你给我滚----滚到远远的地方去！" 她恶狠狠地说，那双绿眼睛冒出了怒火。

170 spawn   

n.卵，产物，后代，结果；vt.产卵，种菌丝于，产生，造成；vi.产卵，大量生产

参考例句：

• The fish were madly pushing their way upstream to spawn.鱼群为产卵而疯狂地向上游挤进。
• These fish will lay spawn in about one month from now.这些鱼大约一个月内会产卵。

171 caterpillar   

n.毛虫，蝴蝶的幼虫

参考例句：

• A butterfly is produced by metamorphosis from a caterpillar.蝴蝶是由毛虫脱胎变成的。
• A caterpillar must pass through the cocoon stage to become a butterfly.毛毛虫必须经过茧的阶段才能变成蝴蝶。

172 parasitic   

adj.寄生的

参考例句：

• Will global warming mean the spread of tropical parasitic diseases?全球变暖是否意味着热带寄生虫病会蔓延呢？
• By definition,this way of life is parasitic.从其含义来说，这是种寄生虫的生活方式。

173 fixed   

adj.固定的，不变的，准备好的；(计算机)固定的

参考例句：

• Have you two fixed on a date for the wedding yet?你们俩选定婚期了吗？
• Once the aim is fixed,we should not change it arbitrarily.目标一旦确定，我们就不应该随意改变。

174 prehensile   

adj.（足等）适于抓握的

参考例句：

• Poets are those strangely prehensile men.诗人是那些具有深刻洞察力的人们。
• A monkey has a prehensile tail.猴子有能盘卷住东西的尾巴。

175 complemental   

补足的，补充的

参考例句：

• When used with complemental ANTIXYGEN JX-DLTP, it has cooperative effect and has extensive uses. 本品与辅助抗氧剂JX-DLTP并用时，具有协同效应，用途极为广泛。
• But through combing, help its grandly a lot of more complemental must module, even talent. 但是通过梳理，盛大帮助其补足了很多必须模块，甚至人才。

176 destitute   

adj.缺乏的；穷困的

参考例句：

• They were destitute of necessaries of life.他们缺少生活必需品。
• They are destitute of common sense.他们缺乏常识。

177 contingent   

adj.视条件而定的；n.一组，代表团，分遣队

参考例句：

• The contingent marched in the direction of the Western Hills.队伍朝西山的方向前进。
• Whether or not we arrive on time is contingent on the weather.我们是否按时到达要视天气情况而定。

178 sketched   

v.草拟（sketch的过去式与过去分词形式）

参考例句：

• The historical article sketched the major events of the decade. 这篇有关历史的文章概述了这十年中的重大事件。 来自《简明英汉词典》
• He sketched the situation in a few vivid words. 他用几句生动的语言简述了局势。 来自《现代汉英综合大词典》

179 worthy   

adj.(of)值得的，配得上的；有价值的

参考例句：

• I did not esteem him to be worthy of trust.我认为他不值得信赖。
• There occurred nothing that was worthy to be mentioned.没有值得一提的事发生。

180 apparently   

adv.显然地；表面上，似乎

参考例句：

• An apparently blind alley leads suddenly into an open space.山穷水尽，豁然开朗。
• He was apparently much surprised at the news.他对那个消息显然感到十分惊异。

181 positively   

adv.明确地，断然，坚决地；实在，确实

参考例句：

• She was positively glowing with happiness.她满脸幸福。
• The weather was positively poisonous.这天气着实讨厌。

182 affected   

adj.不自然的，假装的

参考例句：

• She showed an affected interest in our subject.她假装对我们的课题感到兴趣。
• His manners are affected.他的态度不自然。

183 hereditary   

adj.遗传的，遗传性的，可继承的，世袭的

参考例句：

• The Queen of England is a hereditary ruler.英国女王是世袭的统治者。
• In men,hair loss is hereditary.男性脱发属于遗传。

184 peculiarities   

n. 特质, 特性, 怪癖, 古怪

参考例句：

• the cultural peculiarities of the English 英国人的文化特点
• He used to mimic speech peculiarities of another. 他过去总是模仿别人讲话的特点。

185 cocoon   

n.茧

参考例句：

• A cocoon is a kind of silk covering made by an insect.蚕茧是由昆虫制造的一种由丝组成的外包层。
• The beautiful butterfly emerged from the cocoon.美丽的蝴蝶自茧中出现。

186 domestication   

n.驯养，驯化

参考例句：

• The first was the domestication of animals. 第一个阶段是驯养动物。 来自《简明英汉词典》
• In northwestern China, there is no evidence for endemic domestication of any animals. 在中国西北，没有任何当地动物驯化的迹象。 来自辞典例句

187 conclusive   

adj.最后的，结论的；确凿的，消除怀疑的

参考例句：

• They produced some fairly conclusive evidence.他们提供了一些相当确凿的证据。
• Franklin did not believe that the French tests were conclusive.富兰克林不相信这个法国人的实验是结论性的。

188 eyelid   

n.眼睑，眼皮

参考例句：

• She lifted one eyelid to see what he was doing.她抬起一只眼皮看看他在做什么。
• My eyelid has been tumid since yesterday.从昨天起，我的眼皮就肿了。

189 barbs   

n.（箭头、鱼钩等的）倒钩( barb的名词复数 )；带刺的话；毕露的锋芒；钩状毛

参考例句：

• She slung barbs at me. 她说了些讥刺我的话。 来自《简明英汉词典》
• I would no longer uncomplainingly accept their barbs or allow their unaccountable power to go unchallenged. 我不会再毫无怨言地洗耳恭听他们带刺的话，或让他们的不负责任的权力不受到挑战。 来自辞典例句

190 contingencies   

n.偶然发生的事故，意外事故( contingency的名词复数 )；以备万一

参考例句：

• We must consider all possible contingencies. 我们必须考虑一切可能发生的事。
• We must be prepared for all contingencies. 我们要作好各种准备，以防意外。 来自辞典例句

191 secondly   

adv.第二，其次

参考例句：

• Secondly,use your own head and present your point of view.第二，动脑筋提出自己的见解。
• Secondly it is necessary to define the applied load.其次，需要确定所作用的载荷。

192 locomotion   

n.运动，移动

参考例句：

• By land,air or sea,birds are masters of locomotion.无论是通过陆地，飞越空中还是穿过海洋，鸟应算是运动能手了。
• Food sources also elicit oriented locomotion and recognition behavior patterns in most insects.食物源也引诱大多数昆虫定向迁移和识别行为。

193 obliterated   

v.除去( obliterate的过去式和过去分词 )；涂去；擦掉；彻底破坏或毁灭

参考例句：

• The building was completely obliterated by the bomb. 炸弹把那座建筑物彻底摧毁了。
• He began to drink, drank himself to intoxication, till he slept obliterated. 他一直喝，喝到他快要迷糊地睡着了。 来自《简明英汉词典》

194 incapable   

adj.无能力的，不能做某事的

参考例句：

• He would be incapable of committing such a cruel deed.他不会做出这么残忍的事。
• Computers are incapable of creative thought.计算机不会创造性地思维。

195 demonstration   

n.表明，示范，论证，示威

参考例句：

• His new book is a demonstration of his patriotism.他写的新书是他的爱国精神的证明。
• He gave a demonstration of the new technique then and there.他当场表演了这种新的操作方法。

196 aborted   

adj.流产的，失败的v.（使）流产( abort的过去式和过去分词 )；（使）（某事物）中止；（因故障等而）（使）（飞机、宇宙飞船、导弹等）中断飞行；（使）（飞行任务等）中途失败

参考例句：

• The rocket flight had to be aborted because of difficulties with computer. 因电脑出故障，这次火箭飞行只好中辍。 来自《简明英汉词典》
• They aborted the space flight finally. 他们最后中止了这次宇航飞行。 来自《简明英汉词典》

197 digit   

n.零到九的阿拉伯数字，手指，脚趾

参考例句：

• Her telephone number differs from mine by one digit.她的电话号码和我的只差一个数字。
• Many animals have five digits.许多动物有5趾。

198 lobe   

n.耳垂，（肺，肝等的）叶

参考例句：

• Tiny electrical sensors are placed on your scalp and on each ear lobe.小电器传感器放置在您的头皮和对每个耳垂。
• The frontal lobe of the brain is responsible for controlling movement.大脑前叶的功能是控制行动。

199 rudiments   

n.基础知识，入门

参考例句：

• He has just learned the rudiments of Chinese. 他学汉语刚刚入门。
• You do not seem to know the first rudiments of agriculture. 你似乎连农业上的一点最起码的常识也没有。

200 hind   

adj.后面的，后部的

参考例句：

• The animal is able to stand up on its hind limbs.这种动物能够用后肢站立。
• Don't hind her in her studies.不要在学业上扯她后腿。

201 calves   

n.(calf的复数)笨拙的男子，腓；腿肚子( calf的名词复数 )；牛犊；腓；小腿肚v.生小牛( calve的第三人称单数 )；（冰川）崩解；生（小牛等），产（犊）；使（冰川）崩解

参考例句：

• a cow suckling her calves 给小牛吃奶的母牛
• The calves are grazed intensively during their first season. 小牛在生长的第一季里集中喂养。 来自《简明英汉词典》

202 beaks   

n.鸟嘴( beak的名词复数 )；鹰钩嘴；尖鼻子；掌权者

参考例句：

• Baby cockatoos will have black eyes and soft, almost flexible beaks. 雏鸟凤头鹦鹉黑色的眼睛是柔和的，嘴几乎是灵活的。 来自互联网
• Squid beaks are often found in the stomachs of sperm whales. 经常能在抹香鲸的胃里发现鱿鱼的嘴。 来自互联网

203 soldered   

v.（使）焊接，焊合( solder的过去式和过去分词 )

参考例句：

• Three lead wires are soldered to the anchor terminals. 在固定接线端子上焊有三根导线。 来自辞典例句
• He soldered the broken wires together. 他将断了的电线焊接起来。 来自辞典例句

204 secreted   

v.（尤指动物或植物器官）分泌( secrete的过去式和过去分词 )；隐匿，隐藏

参考例句：

• Insulin is secreted by the pancreas. 胰岛素是胰腺分泌的。
• He secreted his winnings in a drawer. 他把赢来的钱藏在抽届里。 来自《简明英汉词典》

205 hybrid   

n.(动，植）杂种，混合物

参考例句：

• That is a hybrid perpetual rose.那是一株杂交的四季开花的蔷薇。
• The hybrid was tall,handsome,and intelligent.那混血儿高大、英俊、又聪明。

206 essentially   

adv.本质上，实质上，基本上

参考例句：

• Really great men are essentially modest.真正的伟人大都很谦虚。
• She is an essentially selfish person.她本质上是个自私自利的人。

207 perfectly   

adv.完美地，无可非议地，彻底地

参考例句：

• The witnesses were each perfectly certain of what they said.证人们个个对自己所说的话十分肯定。
• Everything that we're doing is all perfectly above board.我们做的每件事情都是光明正大的。

208 pollen   

n.[植]花粉

参考例句：

• Hummingbirds have discovered that nectar and pollen are very nutritious.蜂鸟发现花蜜和花粉是很有营养的。
• He developed an allergy to pollen.他对花粉过敏。

209 stigma   

n.耻辱，污名；(花的)柱头

参考例句：

• Being an unmarried mother used to carry a social stigma.做未婚母亲在社会上曾是不光彩的事。
• The stigma of losing weighed heavily on the team.失败的耻辱让整个队伍压力沉重。

210 nascent   

adj.初生的，发生中的

参考例句：

• That slim book showed the Chinese intelligentsia and the nascent working class.那本小册子讲述了中国的知识界和新兴的工人阶级。
• Despite a nascent democracy movement,there's little traction for direct suffrage.尽管有过一次新生的民主运动，但几乎不会带来直接选举。

211 rhinoceros   

n.犀牛

参考例句：

• The rhinoceros has one horn on its nose.犀牛鼻子上有一个角。
• The body of the rhinoceros likes a cattle and the head likes a triangle.犀牛的形体像牛，头呈三角形。

212 relatively   

adv.比较...地，相对地

参考例句：

• The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
• The operation was relatively painless.手术相对来说不痛。

213 astonishment   

n.惊奇，惊异

参考例句：

• They heard him give a loud shout of astonishment.他们听见他惊奇地大叫一声。
• I was filled with astonishment at her strange action.我对她的奇怪举动不胜惊异。

214 exquisitely   

adv.精致地；强烈地；剧烈地；异常地

参考例句：

• He found her exquisitely beautiful. 他觉得她异常美丽。 来自《简明英汉词典》
• He wore an exquisitely tailored gray silk and accessories to match. 他穿的是做工非常考究的灰色绸缎衣服，还有各种配得很协调的装饰。 来自教父部分

215 revolve   

vi.(使)旋转；循环出现

参考例句：

• The planets revolve around the sun.行星绕着太阳运转。
• The wheels began to revolve slowly.车轮开始慢慢转动。

216 cellular   

adj.移动的；细胞的，由细胞组成的

参考例句：

• She has a cellular telephone in her car.她的汽车里有一部无线通讯电话机。
• Many people use cellular materials as sensitive elements in hygrometers.很多人用蜂窝状的材料作为测量温度的传感元件。

217 calf   

n.小牛，犊，幼仔，小牛皮

参考例句：

• The cow slinked its calf.那头母牛早产了一头小牛犊。
• The calf blared for its mother.牛犊哞哞地高声叫喊找妈妈。

218 stump   

n.残株，烟蒂，讲演台；v.砍断，蹒跚而走

参考例句：

• He went on the stump in his home state.他到故乡所在的州去发表演说。
• He used the stump as a table.他把树桩用作桌子。

219 stumps   

（被砍下的树的）树桩( stump的名词复数 )； 残肢； （板球三柱门的）柱； 残余部分

参考例句：

• Rocks and stumps supplied the place of chairs at the picnic. 野餐时石头和树桩都充当了椅子。
• If you don't stir your stumps, Tom, you'll be late for school again. 汤姆，如果你不快走，上学又要迟到了。

220 vestige   

n.痕迹，遗迹，残余

参考例句：

• Some upright stones in wild places are the vestige of ancient religions.荒原上一些直立的石块是古老宗教的遗迹。
• Every vestige has been swept away.一切痕迹都被一扫而光。

221 vestiges   

残余部分( vestige的名词复数 )； 遗迹； 痕迹； 毫不

参考例句：

• the last vestiges of the old colonial regime 旧殖民制度最后的残余
• These upright stones are the vestiges of some ancient religion. 这些竖立的石头是某种古代宗教的遗迹。

222 manatee   

n.海牛

参考例句：

• We watched dolphin,manatee,sea lion and whale shows.我们看了海豚、海牛、海狮和鲸的表演。
• One of the most extraordinary river creatures is Amazonian manatee.其中河里最特别的生物之一要数亚马孙海牛。

223 dangling   

悬吊着( dangle的现在分词 )； 摆动不定； 用某事物诱惑…； 吊胃口

参考例句：

• The tooth hung dangling by the bedpost, now. 结果，那颗牙就晃来晃去吊在床柱上了。
• The children sat on the high wall,their legs dangling. 孩子们坐在一堵高墙上，摇晃着他们的双腿。

224 abrupt   

adj.突然的，意外的；唐突的，鲁莽的

参考例句：

• The river takes an abrupt bend to the west.这河突然向西转弯。
• His abrupt reply hurt our feelings.他粗鲁的回答伤了我们的感情。

225 caverns   

大山洞，大洞穴( cavern的名词复数 )

参考例句：

• Within were dark caverns; what was inside them, no one could see. 里面是一个黑洞，这里面有什么东西，谁也望不见。 来自汉英文学 - 家（1-26） - 家（1-26）
• UNDERGROUND Under water grottos, caverns Filled with apes That eat figs. 在水帘洞里，挤满了猿争吃无花果。

226 maturity   

n.成熟；完成；(支票、债券等)到期

参考例句：

• These plants ought to reach maturity after five years.这些植物五年后就该长成了。
• This is the period at which the body attains maturity.这是身体发育成熟的时期。

227 obliteration   

n.涂去，删除；管腔闭合

参考例句：

• The policy is obliteration, openly acknowledged. 政策是彻底毁灭，公开承认的政策。 来自演讲部分
• "Obliteration is not a justifiable act of war" “彻底消灭并不是有理的战争行为” 来自演讲部分

228 opposition   

n.反对，敌对

参考例句：

• The party leader is facing opposition in his own backyard.该党领袖在自己的党內遇到了反对。
• The police tried to break down the prisoner's opposition.警察设法制住了那个囚犯的反抗。

229 applied   

adj.应用的；v.应用，适用

参考例句：

• She plans to take a course in applied linguistics.她打算学习应用语言学课程。
• This cream is best applied to the face at night.这种乳霜最好晚上擦脸用。

230 hesitation   

n.犹豫，踌躇

参考例句：

• After a long hesitation, he told the truth at last.踌躇了半天，他终于直说了。
• There was a certain hesitation in her manner.她的态度有些犹豫不决。