And here, as it will always happen when dealing6 with an extensive subject, the greater part of my course — if, indeed, so small a number of lectures can be properly called a course — must be devoted7 to preliminary matters, or rather to a statement of those facts and of those principles which the work itself dwells upon, and brings more or less directly before us. I have no right to suppose that all or any of you are naturalists8; and even if you were, the misconceptions and misunderstandings prevalent even among naturalists on these matters would make it desirable that I should take the course I now propose to take — that I should start from the beginning — that I should endeavour to point out what is the existing state of the organic world — that I should point out its past condition — that I should state what is the precise nature of the undertaking9 which Mr. Darwin has taken in hand; that I should endeavour to show you what are the only methods by which that undertaking can be brought to an issue, and to point out to you how far the author of the work in question has satisfied those conditions, how far he has not satisfied them, how far they are satisfiable by man, and how far they are not satisfiable by man.
To-night, in taking up the first part of this question, I shall endeavour to put before you a sort of broad notion of our knowledge of the condition of the living world. There are many ways of doing this. I might deal with it pictorially10 and graphically11. Following the example of Humboldt in his “Aspects of Nature”, I might endeavour to point out the infinite variety of organic life in every mode of its existence, with reference to the variations of climate and the like; and such an attempt would be fraught13 with interest to us all; but considering the subject before us, such a course would not be that best calculated to assist us. In an argument of this kind we must go further and dig deeper into the matter; we must endeavour to look into the foundations of living Nature, if I may so say, and discover the principles involved in some of her most secret operations. I propose, therefore, in the first place, to take some ordinary animal with which you are all familiar, and, by easily comprehensible and obvious examples drawn15 from it, to show what are the kind of problems which living beings in general lay before us; and I shall then show you that the same problems are laid open to us by all kinds of living beings. But first, let me say in what sense I have used the words “organic nature.” In speaking of the causes which lead to our present knowledge of organic nature, I have used it almost as an equivalent of the word “living,” and for this reason — that in almost all living beings you can distinguish several distinct portions set apart to do particular things and work in a particular way. These are termed “organs,” and the whole together is called “organic.” And as it is universally characteristic of them, this term “organic” has been very conveniently employed to denote the whole of living nature — the whole of the plant world, and the whole of the animal world.
Few animals can be more familiar to you than that whose skeleton is shown on our diagram. You need not bother yourselves with this “Equus caballus” written under it; that is only the Latin name of it, and does not make it any better. It simply means the common Horse. Suppose we wish to understand all about the Horse. Our first object must be to study the structure of the animal. The whole of his body is inclosed within a hide, a skin covered with hair; and if that hide or skin be taken off, we find a great mass of flesh, or what is technically16 called muscle, being the substance which by its power of contraction17 enables the animal to move. These muscles move the hard parts one upon the other, and so give that strength and power of motion which renders the Horse so useful to us in the performance of those services in which we employ him.
And then, on separating and removing the whole of this skin and flesh, you have a great series of bones, hard structures, bound together with ligaments, and forming the skeleton which is represented here.
[FIGURE 1. (Section through a horse.)
FIGURE 2. (Section through a cell.)]
In that skeleton there are a number of parts to be recognized. The long series of bones, beginning from the skull19 and ending in the tail, is called the spine20, and those in front are the ribs21; and then there are two pairs of limbs, one before and one behind; and there are what we all know as the fore1-legs and the hind-legs. If we pursue our researches into the interior of this animal, we find within the framework of the skeleton a great cavity, or rather, I should say, two great cavities — one cavity beginning in the skull and running through the neck-bones, along the spine, and ending in the tail, containing the brain and the spinal22 marrow23, which are extremely important organs. The second great cavity, commencing with the mouth, contains the gullet, the stomach, the long intestine24, and all the rest of those internal apparatus25 which are essential for digestion26; and then in the same great cavity, there are lodged27 the heart and all the great vessels28 going from it; and, besides that, the organs of respiration29 — the lungs: and then the kidneys, and the organs of reproduction, and so on. Let us now endeavour to reduce this notion of a horse that we now have, to some such kind of simple expression as can be at once, and without difficulty, retained in the mind, apart from all minor30 details. If I make a transverse section, that is, if I were to saw a dead horse across, I should find that, if I left out the details, and supposing I took my section through the anterior31 region, and through the fore-limbs, I should have here this kind of section of the body (Fig18. 1). Here would be the upper part of the animal — that great mass of bones that we spoke32 of as the spine (a, Fig. 1). Here I should have the alimentary33 canal (b, Fig. 1). Here I should have the heart (c, Fig. 1); and then you see, there would be a kind of double tube, the whole being inclosed within the hide; the spinal marrow would be placed in the upper tube (a, Fig. 1), and in the lower tube (d d, Fig. 1), there would be the alimentary canal (b), and the heart (c); and here I shall have the legs proceeding34 from each side. For simplicity35’s sake, I represent them merely as stumps37 (e e, Fig. 1). Now that is a horse — as mathematicians38 would say — reduced to its most simple expression. Carry that in your minds, if you please, as a simplified idea of the structure of the Horse. The considerations which I have now put before you belong to what we technically call the ‘Anatomy39’ of the Horse. Now, suppose we go to work upon these several parts — flesh and hair, and skin and bone, and lay open these various organs with our scalpels, and examine them by means of our magnifying — glasses, and see what we can make of them. We shall find that the flesh is made up of bundles of strong fibres. The brain and nerves, too, we shall find, are made up of fibres, and these queer-looking things that are called ganglionic corpuscles. If we take a slice of the bone and examine it, we shall find that it is very like this diagram of a section of the bone of an ostrich40, though differing, of course, in some details; and if we take any part whatsoever41 of the tissue, and examine it, we shall find it all has a minute structure, visible only under the microscope. All these parts constitute microscopic42 anatomy or ‘Histology.’ These parts are constantly being changed; every part is constantly growing, decaying, and being replaced during the life of the animal. The tissue is constantly replaced by new material; and if you go back to the young state of the tissue in the case of muscle, or in the case of skin, or any of the organs I have mentioned, you will find that they all come under the same condition. Every one of these microscopic filaments43 and fibres (I now speak merely of the general character of the whole process)— every one of these parts — could be traced down to some modification44 of a tissue which can be readily divided into little particles of fleshy matter, of that substance which is composed of the chemical elements, carbon, hydrogen, oxygen, and nitrogen, having such a shape as this (Fig. 2). These particles, into which all primitive45 tissues break up, are called cells. If I were to make a section of a piece of the skin of my hand, I should find that it was made up of these cells. If I examine the fibres which form the various organs of all living animals, I should find that all of them, at one time or other, had been formed out of a substance consisting of similar elements; so that you see, just as we reduced the whole body in the gross to that sort of simple expression given in Fig. 1, so we may reduce the whole of the microscopic structural46 elements to a form of even greater simplicity; just as the plan of the whole body may be so represented in a sense (Fig. 1), so the primary structure of every tissue may be represented by a mass of cells (Fig. 2).
Having thus, in this sort of general way, sketched48 to you what I may call, perhaps, the architecture of the body of the Horse (what we term technically its Morphology), I must now turn to another aspect. A horse is not a mere36 dead structure: it is an active, living, working machine. Hitherto we have, as it were, been looking at a steam-engine with the fires out, and nothing in the boiler49; but the body of the living animal is a beautifully-formed active machine, and every part has its different work to do in the working of that machine, which is what we call its life. The Horse, if you see him after his day’s work is done, is cropping the grass in the fields, as it may be, or munching50 the oats in his stable. What is he doing? His jaws51 are working as a mill — and a very complex mill too — grinding the corn, or crushing the grass to a pulp52. As soon as that operation has taken place, the food is passed down to the stomach, and there it is mixed with the chemical fluid called the gastric53 juice, a substance which has the peculiar54 property of making soluble55 and dissolving out the nutritious56 matter in the grass, and leaving behind those parts which are not nutritious; so that you have, first, the mill, then a sort of chemical digester; and then the food, thus partially57 dissolved, is carried back by the muscular contractions58 of the intestines59 into the hinder parts of the body, while the soluble portions are taken up into the blood. The blood is contained in a vast system of pipes, spreading through the whole body, connected with a force pump — the heart — which, by its position and by the contractions of its valves, keeps the blood constantly circulating in one direction, never allowing it to rest; and then, by means of this circulation of the blood, laden60 as it is with the products of digestion, the skin, the flesh, the hair, and every other part of the body, draws from it that which it wants, and every one of these organs derives61 those materials which are necessary to enable it to do its work.
The action of each of these organs, the performance of each of these various duties, involve in their operation a continual absorption of the matters necessary for their support, from the blood, and a constant formation of waste products, which are returned to the blood, and conveyed by it to the lungs and the kidneys, which are organs that have allotted62 to them the office of extracting, separating, and getting rid of these waste products; and thus the general nourishment63, labour, and repair of the whole machine is kept up with order and regularity64. But not only is it a machine which feeds and appropriates to its own support the nourishment necessary to its existence — it is an engine for locomotive purposes. The Horse desires to go from one place to another; and to enable it to do this, it has those strong contractile bundles of muscles attached to the bones of its limbs, which are put in motion by means of a sort of telegraphic apparatus formed by the brain and the great spinal cord running through the spine or backbone65; and to this spinal cord are attached a number of fibres termed nerves, which proceed to all parts of the structure. By means of these the eyes, nose, tongue, and skin — all the organs of perception — transmit impressions or sensations to the brain, which acts as a sort of great central telegraph-office, receiving impressions and sending messages to all parts of the body, and putting in motion the muscles necessary to accomplish any movement that may be desired. So that you have here an extremely complex and beautifully-proportioned machine, with all its parts working harmoniously66 together towards one common object — the preservation67 of the life of the animal.
Now, note this: the Horse makes up its waste by feeding, and its food is grass or oats, or perhaps other vegetable products; therefore, in the long run, the source of all this complex machinery68 lies in the vegetable kingdom. But where does the grass, or the oat, or any other plant, obtain this nourishing food-producing material? At first it is a little seed, which soon begins to draw into itself from the earth and the surrounding air matters which in themselves contain no vital properties whatever; it absorbs into its own substance water, an inorganic69 body; it draws into its substance carbonic acid, an inorganic matter; and ammonia, another inorganic matter, found in the air; and then, by some wonderful chemical process, the details of which chemists do not yet understand, though they are near foreshadowing them, it combines them into one substance, which is known to us as ‘Protein,’ a complex compound of carbon, hydrogen, oxygen, and nitrogen, which alone possesses the property of manifesting vitality70 and of permanently71 supporting animal life. So that, you see, the waste products of the animal economy, the effete72 materials which are continually being thrown off by all living beings, in the form of organic matters, are constantly replaced by supplies of the necessary repairing and rebuilding materials drawn from the plants, which in their turn manufacture them, so to speak, by a mysterious combination of those same inorganic materials.
Let us trace out the history of the Horse in another direction. After a certain time, as the result of sickness or disease, the effect of accident, or the consequence of old age, sooner or later, the animal dies. The multitudinous operations of this beautiful mechanism73 flag in their performance, the Horse loses its vigour74, and after passing through the curious series of changes comprised in its formation and preservation, it finally decays, and ends its life by going back into that inorganic world from which all but an inappreciable fraction of its substance was derived75. Its bones become mere carbonate and phosphate of lime; the matter of its flesh, and of its other parts, becomes, in the long run, converted into carbonic acid, into water, and into ammonia. You will now, perhaps, understand the curious relation of the animal with the plant, of the organic with the inorganic world, which is shown in this diagram (Fig. 3).
[FIGURE 3. (Diagram showing material relationship of the Vegetable, Animal and Inorganic Worlds.)]
The plant gathers these inorganic materials together and makes them up into its own substance. The animal eats the plant and appropriates the nutritious portions to its own sustenance76, rejects and gets rid of the useless matters; and, finally, the animal itself dies, and its whole body is decomposed77 and returned into the inorganic world. There is thus a constant circulation from one to the other, a continual formation of organic life from inorganic matters, and as constant a return of the matter of living bodies to the inorganic world; so that the materials of which our bodies are composed are largely, in all probability, the substances which constituted the matter of long extinct creations, but which have in the interval78 constituted a part of the inorganic world.
Thus we come to the conclusion, strange at first sight, that the MATTER constituting the living world is identical with that which forms the inorganic world. And not less true is it that, remarkable79 as are the powers or, in other words, as are the FORCES which are exerted by living beings, yet all these forces are either identical with those which exist in the inorganic world, or they are convertible80 into them; I mean in just the same sense as the researches of physical philosophers have shown that heat is convertible into electricity, that electricity is convertible into magnetism81, magnetism into mechanical force or chemical force, and any one of them with the other, each being measurable in terms of the other — even so, I say, that great law is applicable to the living world. Consider why is the skeleton of this horse capable of supporting the masses of flesh and the various organs forming the living body, unless it is because of the action of the same forces of cohesion82 which combines together the particles of matter composing this piece of chalk? What is there in the muscular contractile power of the animal but the force which is expressible, and which is in a certain sense convertible, into the force of gravity which it overcomes? Or, if you go to more hidden processes, in what does the process of digestion differ from those processes which are carried on in the laboratory of the chemist? Even if we take the most recondite83 and most complex operations of animal life — those of the nervous system, these of late years have been shown to be — I do not say identical in any sense with the electrical processes — but this has been shown, that they are in some way or other associated with them; that is to say, that every amount of nervous action is accompanied by a certain amount of electrical disturbance84 in the particles of the nerves in which that nervous action is carried on. In this way the nervous action is related to electricity in the same way that heat is related to electricity; and the same sort of argument which demonstrates the two latter to be related to one another shows that the nervous forces are correlated to electricity; for the experiments of M. Dubois Reymond and others have shown that whenever a nerve is in a state of excitement, sending a message to the muscles or conveying an impression to the brain, there is a disturbance of the electrical condition of that nerve which does not exist at other times; and there are a number of other facts and phenomena85 of that sort; so that we come to the broad conclusion that not only as to living matter itself, but as to the forces that matter exerts, there is a close relationship between the organic and the inorganic world — the difference between them arising from the diverse combination and disposition86 of identical forces, and not from any primary diversity, so far as we can see.
I said just now that the Horse eventually died and became converted into the same inorganic substances from whence all but an inappreciable fraction of its substance demonstrably originated, so that the actual wanderings of matter are as remarkable as the transmigrations of the soul fabled87 by Indian tradition. But before death has occurred, in the one sex or the other, and in fact in both, certain products or parts of the organism have been set free, certain parts of the organisms of the two sexes have come into contact with one another, and from that conjunction, from that union which then takes place, there results the formation of a new being. At stated times the mare88, from a particular part of the interior of her body, called the ovary, gets rid of a minute particle of matter comparable in all essential respects with that which we called a cell a little while since, which cell contains a kind of nucleus89 in its centre, surrounded by a clear space and by a viscid mass of protein substance (Fig. 2); and though it is different in appearance from the eggs which we are mostly acquainted with, it is really an egg. After a time this minute particle of matter, which may only be a small fraction of a grain in weight, undergoes a series of changes — wonderful, complex changes. Finally, upon its surface there is fashioned a little elevation90, which afterwards becomes divided and marked by a groove91. The lateral92 boundaries of the groove extend upwards93 and downwards94, and at length give rise to a double tube. In the upper smaller tube the spinal marrow and brain are fashioned; in the lower, the alimentary canal and heart; and at length two pairs of buds shoot out at the sides of the body, which are the rudiments95 of the limbs. In fact a true drawing of a section of the embryo96 in this state would in all essential respects resemble that diagram of a horse reduced to its simplest expression, which I first placed before you (Fig. 1).
Slowly and gradually these changes take place. The whole of the body, at first, can be broken up into “cells,” which become in one place metamorphosed into muscle — in another place into gristle and bone — in another place into fibrous tissue — and in another into hair; every part becoming gradually and slowly fashioned, as if there were an artificer at work in each of these complex structures that we have mentioned. This embryo, as it is called, then passes into other conditions. I should tell you that there is a time when the embryos97 of neither dog, nor horse, nor porpoise98, nor monkey, nor man, can be distinguished99 by any essential feature one from the other; there is a time when they each and all of them resemble this one of the Dog. But as development advances, all the parts acquire their speciality, till at length you have the embryo converted into the form of the parent from which it started. So that you see, this living animal, this horse, begins its existence as a minute particle of nitrogenous matter, which, being supplied with nutriment (derived, as I have shown, from the inorganic world), grows up according to the special type and construction of its parents, works and undergoes a constant waste, and that waste is made good by nutriment derived from the inorganic world; the waste given off in this way being directly added to the inorganic world; and eventually the animal itself dies, and, by the process of decomposition100, its whole body is returned to those conditions of inorganic matter in which its substance originated.
This, then, is that which is true of every living form, from the lowest plant to the highest animal — to man himself. You might define the life of every one in exactly the same terms as those which I have now used; the difference between the highest and the lowest being simply in the complexity101 of the developmental changes, the variety of the structural forms, the diversity of the physiological102 functions which are exerted by each.
If I were to take an oak tree as a specimen103 of the plant world, I should find that it originated in an acorn104, which, too, commenced in a cell; the acorn is placed in the ground, and it very speedily begins to absorb the inorganic matters I have named, adds enormously to its bulk, and we can see it, year after year, extending itself upward and downward, attracting and appropriating to itself inorganic materials, which it vivifies, and eventually, as it ripens105, gives off its own proper acorns106, which again run the same course. But I need not multiply examples — from the highest to the lowest the essential features of life are the same, as I have described in each of these cases.
So much, then, for these particular features of the organic world, which you can understand and comprehend, so long as you confine yourself to one sort of living being, and study that only.
But, as you know, horses are not the only living creatures in the world; and again, horses, like all other animals, have certain limits — are confined to a certain area on the surface of the earth on which we live — and, as that is the simpler matter, I may take that first. In its wild state, and before the discovery of America, when the natural state of things was interfered107 with by the Spaniards, the Horse was only to be found in parts of the earth which are known to geographers108 as the Old World; that is to say, you might meet with horses in Europe, Asia, or Africa; but there were none in Australia, and there were none whatsoever in the whole continent of America, from Labrador down to Cape109 Horn. This is an empirical fact, and it is what is called, stated in the way I have given it you, the ‘Geographical110 Distribution’ of the Horse.
Why horses should be found in Europe, Asia, and Africa, and not in America, is not obvious; the explanation that the conditions of life in America are unfavourable to their existence, and that, therefore, they had not been created there, evidently does not apply; for when the invading Spaniards, or our own yeomen farmers, conveyed horses to these countries for their own use, they were found to thrive well and multiply very rapidly; and many are even now running wild in those countries, and in a perfectly111 natural condition. Now, suppose we were to do for every animal what we have here done for the Horse — that is, to mark off and distinguish the particular district or region to which each belonged; and supposing we tabulated112 all these results, that would be called the Geographical Distribution of animals, while a corresponding study of plants would yield as a result the Geographical Distribution of plants.
I pass on from that now, as I merely wished to explain to you what I meant by the use of the term ‘Geographical Distribution.’ As I said, there is another aspect, and a much more important one, and that is, the relations of the various animals to one another. The Horse is a very well-defined matter-of-fact sort of animal, and we are all pretty familiar with its structure. I dare say it may have struck you, that it resembles very much no other member of the animal kingdom, except perhaps the Zebra or the Ass14. But let me ask you to look along these diagrams. Here is the skeleton of the Horse, and here the skeleton of the Dog. You will notice that we have in the Horse a skull, a backbone and ribs, shoulder-blades and haunch-bones. In the fore-limb, one upper arm-bone, two fore arm-bones, wrist-bones (wrongly called knee), and middle hand-bones, ending in the three bones of a finger, the last of which is sheathed113 in the horny hoof114 of the fore-foot: in the hind-limb, one thigh-bone, two leg-bones, anklebones, and middle foot-bones, ending in the three bones of a toe, the last of which is encased in the hoof of the hind-foot. Now turn to the Dog’s skeleton. We find identically the same bones, but more of them, there being more toes in each foot, and hence more toe-bones.
Well, that is a very curious thing! The fact is that the Dog and the Horse — when one gets a look at them without the outward impediments of the skin — are found to be made in very much the same sort of fashion. And if I were to make a transverse section of the Dog, I should find the same organs that I have already shown you as forming parts of the Horse. Well, here is another skeleton — that of a kind of Lemur — you see he has just the same bones; and if I were to make a transverse section of it, it would be just the same again. In your mind’s eye turn him round, so as to put his backbone in a position inclined obliquely115 upwards and forwards, just as in the next three diagrams, which represent the skeletons of an Orang, a Chimpanzee, a Gorilla116, and you find you have no trouble in identifying the bones throughout; and lastly turn to the end of the series, the diagram representing a man’s skeleton, and still you find no great structural feature essentially117 altered. There are the same bones in the same relations. From the Horse we pass on and on, with gradual steps, until we arrive at last at the highest known forms. On the other hand, take the other line of diagrams, and pass from the Horse downwards in the scale to this fish; and still, though the modifications118 are vastly greater, the essential framework of the organization remains119 unchanged. Here, for instance, is a Porpoise: here is its strong backbone, with the cavity running through it, which contains the spinal cord; here are the ribs, here the shoulder blade; here is the little short upper-arm bone, here are the two forearm bones, the wrist-bone, and the finger-bones.
Strange, is it not, that the Porpoise should have in this queer-looking affair — its flapper (as it is called), the same fundamental elements as the fore-leg of the Horse or the Dog, or the Ape or Man; and here you will notice a very curious thing — the hinder limbs are absent. Now, let us make another jump. Let us go to the Codfish: here you see is the forearm, in this large pectoral fin12 — carrying your mind’s eye onward120 from the flapper of the Porpoise. And here you have the hinder limbs restored in the shape of these ventral fins121. If I were to make a transverse section of this, I should find just the same organs that we have before noticed. So that, you see, there comes out this strange conclusion as the result of our investigations122, that the Horse, when examined and compared with other animals, is found by no means to stand alone in nature; but that there are an enormous number of other creatures which have backbones123, ribs, and legs, and other parts arranged in the same general manner, and in all their formation exhibiting the same broad peculiarities124.
I am sure that you cannot have followed me even in this extremely elementary exposition of the structural relations of animals, without seeing what I have been driving at all through, which is, to show you that, step by step, naturalists have come to the idea of a unity125 of plan, or conformity126 of construction, among animals which appeared at first sight to be extremely dissimilar.
And here you have evidence of such a unity of plan among all the animals which have backbones, and which we technically call “Vertebrata”. But there are multitudes of other animals, such as crabs127, lobsters128, spiders, and so on, which we term “Annulosa”. In these I could not point out to you the parts that correspond with those of the Horse — the backbone, for instance — as they are constructed upon a very different principle, which is also common to all of them; that is to say, the Lobster129, the Spider, and the Centipede, have a common plan running through their whole arrangement, in just the same way that the Horse, the Dog, and the Porpoise assimilate to each other.
Yet other creatures — whelks, cuttlefishes, oysters131, snails132, and all their tribe (“Mollusca”)— resemble one another in the same way, but differ from both “Vertebrata” and “Annulosa”; and the like is true of the animals called “Coelenterata” (Polypes) and “Protozoa” (animalcules and sponges).
Now, by pursuing this sort of comparison, naturalists have arrived at the conviction that there are — some think five, and some seven — but certainly not more than the latter number — and perhaps it is simpler to assume five — distinct plans or constructions in the whole of the animal world; and that the hundreds of thousands of species of creatures on the surface of the earth, are all reducible to those five, or, at most, seven, plans of organization.
But can we go no further than that? When one has got so far, one is tempted133 to go on a step and inquire whether we cannot go back yet further and bring down the whole to modifications of one primordial134 unit. The anatomist cannot do this; but if he call to his aid the study of development, he can do it. For we shall find that, distinct as those plans are, whether it be a porpoise or man, or lobster, or any of those other kinds I have mentioned, every one begins its existence with one and the same primitive form — that of the egg, consisting, as we have seen, of a nitrogenous substance, having a small particle or nucleus in the centre of it. Furthermore, the earlier changes of each are substantially the same. And it is in this that lies that true “unity of organization” of the animal kingdom which has been guessed at and fancied for many years; but which it has been left to the present time to be demonstrated by the careful study of development. But is it possible to go another step further still, and to show that in the same way the whole of the organic world is reducible to one primitive condition of form? Is there among the plants the same primitive form of organization, and is that identical with that of the animal kingdom? The reply to that question, too, is not uncertain or doubtful. It is now proved that every plant begins its existence under the same form; that is to say, in that of a cell — a particle of nitrogenous matter having substantially the same conditions. So that if you trace back the oak to its first germ, or a man, or a horse, or lobster, or oyster130, or any other animal you choose to name, you shall find each and all of these commencing their existence in forms essentially similar to each other: and, furthermore, that the first processes of growth, and many of the subsequent modifications, are essentially the same in principle in almost all.
In conclusion, let me, in a few words, recapitulate135 the positions which I have laid down. And you must understand that I have not been talking mere theory; I have been speaking of matters which are as plainly demonstrable as the commonest propositions of Euclid — of facts that must form the basis of all speculations136 and beliefs in Biological science. We have gradually traced down all organic forms, or, in other words, we have analyzed137 the present condition of animated138 nature, until we found that each species took its origin in a form similar to that under which all the others commence their existence. We have found the whole of the vast array of living forms, with which we are surrounded, constantly growing, increasing, decaying and disappearing; the animal constantly attracting, modifying, and applying to its sustenance the matter of the vegetable kingdom, which derived its support from the absorption and conversion139 of inorganic matter. And so constant and universal is this absorption, waste, and reproduction, that it may be said with perfect certainty that there is left in no one of our bodies at the present moment a millionth part of the matter of which they were originally formed! We have seen, again, that not only is the living matter derived from the inorganic world, but that the forces of that matter are all of them correlative with and convertible into those of inorganic nature.
This, for our present purposes, is the best view of the present condition of organic nature which I can lay before you: it gives you the great outlines of a vast picture, which you must fill up by your own study.
In the next lecture I shall endeavour in the same way to go back into the past, and to sketch47 in the same broad manner the history of life in epochs preceding our own.
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| n.博物学家( naturalist的名词复数 )；（文学艺术的）自然主义者 | |
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undertaking
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| n.保证，许诺，事业 | |
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10
pictorially
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| 绘画般地 | |
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graphically
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| adv.通过图表；生动地，轮廓分明地 | |
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fin
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| n.鳍；(飞机的)安定翼 | |
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fraught
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| adj.充满…的，伴有(危险等)的；忧虑的 | |
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ass
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| n.驴；傻瓜，蠢笨的人 | |
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15
drawn
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| v.拖，拉，拔出；adj.憔悴的，紧张的 | |
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technically
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| adv.专门地，技术上地 | |
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17
contraction
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| n.缩略词，缩写式，害病 | |
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18
fig
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| n.无花果(树) | |
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19
skull
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| n.头骨；颅骨 | |
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20
spine
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| n.脊柱，脊椎；(动植物的)刺；书脊 | |
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21
ribs
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| n.肋骨( rib的名词复数 )；（船或屋顶等的）肋拱；肋骨状的东西；（织物的）凸条花纹 | |
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22
spinal
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| adj.针的，尖刺的，尖刺状突起的；adj.脊骨的，脊髓的 | |
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23
marrow
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| n.骨髓；精华；活力 | |
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24
intestine
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| adj.内部的；国内的；n.肠 | |
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25
apparatus
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| n.装置，器械；器具，设备 | |
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26
digestion
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| n.消化，吸收 | |
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27
lodged
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| v.存放( lodge的过去式和过去分词 )；暂住；埋入；（权利、权威等）归属 | |
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28
vessels
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| n.血管( vessel的名词复数 )；船；容器；（具有特殊品质或接受特殊品质的）人 | |
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29
respiration
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| n.呼吸作用；一次呼吸；植物光合作用 | |
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30
minor
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| adj.较小(少)的，较次要的；n.辅修学科；vi.辅修 | |
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31
anterior
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| adj.较早的；在前的 | |
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32
spoke
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| n.（车轮的）辐条；轮辐；破坏某人的计划；阻挠某人的行动 v.讲，谈（speak的过去式）；说；演说；从某种观点来说 | |
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33
alimentary
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| adj.饮食的，营养的 | |
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34
proceeding
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| n.行动，进行，(pl.)会议录，学报 | |
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35
simplicity
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| n.简单，简易；朴素；直率，单纯 | |
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36
mere
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| adj.纯粹的；仅仅，只不过 | |
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37
stumps
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| （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 | |
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38
mathematicians
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| 数学家( mathematician的名词复数 ) | |
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39
anatomy
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| n.解剖学，解剖；功能，结构，组织 | |
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40
ostrich
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| n.鸵鸟 | |
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41
whatsoever
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| adv.（用于否定句中以加强语气）任何；pron.无论什么 | |
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42
microscopic
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| adj.微小的，细微的，极小的，显微的 | |
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43
filaments
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| n.（电灯泡的）灯丝( filament的名词复数 )；丝极；细丝；丝状物 | |
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44
modification
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| n.修改，改进，缓和，减轻 | |
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45
primitive
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| adj.原始的；简单的；n.原(始)人，原始事物 | |
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46
structural
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| adj.构造的，组织的，建筑（用）的 | |
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47
sketch
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| n.草图；梗概；素描；v.素描；概述 | |
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48
sketched
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| v.草拟（sketch的过去式与过去分词形式） | |
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49
boiler
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| n.锅炉；煮器(壶，锅等) | |
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50
munching
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| v.用力咀嚼（某物），大嚼( munch的现在分词 ) | |
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51
jaws
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| n.口部；嘴 | |
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52
pulp
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| n.果肉，纸浆；v.化成纸浆，除去...果肉，制成纸浆 | |
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53
gastric
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| adj.胃的 | |
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54
peculiar
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| adj.古怪的，异常的；特殊的，特有的 | |
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55
soluble
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| adj.可溶的；可以解决的 | |
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56
nutritious
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| adj.有营养的，营养价值高的 | |
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57
partially
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| adv.部分地，从某些方面讲 | |
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58
contractions
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| n.收缩( contraction的名词复数 )；缩减；缩略词；（分娩时）子宫收缩 | |
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59
intestines
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| n.肠( intestine的名词复数 ) | |
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60
laden
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| adj.装满了的；充满了的；负了重担的；苦恼的 | |
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61
derives
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| v.得到( derive的第三人称单数 )；（从…中）得到获得；源于；（从…中）提取 | |
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62
allotted
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| 分配，拨给，摊派( allot的过去式和过去分词 ) | |
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63
nourishment
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| n.食物，营养品；营养情况 | |
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64
regularity
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| n.规律性，规则性；匀称，整齐 | |
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65
backbone
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| n.脊骨，脊柱，骨干；刚毅，骨气 | |
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66
harmoniously
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| 和谐地，调和地 | |
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67
preservation
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| n.保护，维护，保存，保留，保持 | |
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68
machinery
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| n.(总称)机械，机器；机构 | |
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69
inorganic
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| adj.无生物的；无机的 | |
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70
vitality
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| n.活力，生命力，效力 | |
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71
permanently
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| adv.永恒地，永久地，固定不变地 | |
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72
effete
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| adj.无生产力的，虚弱的 | |
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73
mechanism
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| n.机械装置；机构，结构 | |
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74
vigour
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| （=vigor）n.智力，体力，精力 | |
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75
derived
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| 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 | |
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76
sustenance
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| n.食物，粮食；生活资料；生计 | |
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77
decomposed
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| 已分解的，已腐烂的 | |
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78
interval
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| n.间隔，间距；幕间休息，中场休息 | |
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79
remarkable
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| adj.显著的，异常的，非凡的，值得注意的 | |
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80
convertible
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| adj.可改变的，可交换，同意义的；n.有活动摺篷的汽车 | |
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81
magnetism
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| n.磁性，吸引力，磁学 | |
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82
cohesion
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| n.团结，凝结力 | |
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83
recondite
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| adj.深奥的，难解的 | |
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84
disturbance
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| n.动乱，骚动；打扰，干扰；(身心)失调 | |
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85
phenomena
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| n.现象 | |
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86
disposition
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| n.性情，性格；意向，倾向；排列，部署 | |
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87
fabled
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| adj.寓言中的，虚构的 | |
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88
mare
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| n.母马，母驴 | |
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89
nucleus
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| n.核，核心，原子核 | |
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90
elevation
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| n.高度；海拔；高地；上升；提高 | |
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91
groove
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| n.沟，槽；凹线，（刻出的）线条，习惯 | |
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92
lateral
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| adj.侧面的，旁边的 | |
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93
upwards
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| adv.向上，在更高处...以上 | |
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94
downwards
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| adj./adv.向下的（地），下行的（地） | |
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95
rudiments
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| n.基础知识，入门 | |
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96
embryo
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| n.胚胎，萌芽的事物 | |
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97
embryos
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| n.晶胚；胚，胚胎( embryo的名词复数 ) | |
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98
porpoise
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| n.鼠海豚 | |
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99
distinguished
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| adj.卓越的，杰出的，著名的 | |
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100
decomposition
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| n. 分解, 腐烂, 崩溃 | |
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101
complexity
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| n.复杂(性)，复杂的事物 | |
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102
physiological
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| adj.生理学的，生理学上的 | |
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103
specimen
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| n.样本，标本 | |
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104
acorn
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| n.橡实，橡子 | |
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105
ripens
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| v.成熟，使熟( ripen的第三人称单数 ) | |
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106
acorns
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| n.橡子，栎实( acorn的名词复数 ) | |
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107
interfered
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| v.干预( interfere的过去式和过去分词 )；调停；妨碍；干涉 | |
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108
geographers
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| 地理学家( geographer的名词复数 ) | |
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109
cape
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| n.海角，岬；披肩，短披风 | |
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110
geographical
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| adj.地理的；地区(性)的 | |
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111
perfectly
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| adv.完美地，无可非议地，彻底地 | |
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112
tabulated
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| 把（数字、事实）列成表( tabulate的过去式和过去分词 ) | |
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113
sheathed
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| adj.雕塑像下半身包在鞘中的；覆盖的；铠装的；装鞘了的v.将（刀、剑等）插入鞘( sheathe的过去式和过去分词 )；包，覆盖 | |
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114
hoof
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| n.(马，牛等的)蹄 | |
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115
obliquely
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| adv.斜； 倾斜； 间接； 不光明正大 | |
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116
gorilla
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| n.大猩猩，暴徒，打手 | |
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117
essentially
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| adv.本质上，实质上，基本上 | |
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118
modifications
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| n.缓和( modification的名词复数 )；限制；更改；改变 | |
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119
remains
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| n.剩余物，残留物；遗体，遗迹 | |
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120
onward
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| adj.向前的，前进的；adv.向前，前进，在先 | |
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121
fins
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| [医]散热片；鱼鳍；飞边；鸭掌 | |
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122
investigations
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| （正式的）调查( investigation的名词复数 )； 侦查； 科学研究； 学术研究 | |
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123
backbones
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| n.骨干( backbone的名词复数 )；脊骨；骨气；脊骨状物 | |
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124
peculiarities
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| n. 特质, 特性, 怪癖, 古怪 | |
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125
unity
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| n.团结，联合，统一；和睦，协调 | |
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126
conformity
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| n.一致，遵从，顺从 | |
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127
crabs
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| 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 ) | |
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128
lobsters
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| 龙虾( lobster的名词复数 )； 龙虾肉 | |
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129
lobster
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| n.龙虾，龙虾肉 | |
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130
oyster
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| n.牡蛎；沉默寡言的人 | |
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131
oysters
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| 牡蛎( oyster的名词复数 ) | |
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132
snails
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| n.蜗牛；迟钝的人；蜗牛( snail的名词复数 ) | |
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133
tempted
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| v.怂恿（某人）干不正当的事；冒…的险（tempt的过去分词） | |
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134
primordial
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| adj.原始的；最初的 | |
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135
recapitulate
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| v.节述要旨，择要说明 | |
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136
speculations
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| n.投机买卖( speculation的名词复数 )；思考；投机活动；推断 | |
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137
analyzed
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| v.分析( analyze的过去式和过去分词 )；分解；解释；对…进行心理分析 | |
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138
animated
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| adj.生气勃勃的，活跃的，愉快的 | |
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conversion
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| n.转化，转换，转变 | |
参考例句： |
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