What has occurred in the Fishing-frog is the reverse of what has occurred in the other instances just given. For here the anterior6 and broad part of the body is not of a fleshy character, and so all the fleshy substance which has been thence diverted has been placed by nature in the tail and hinder portion of the body.
In fishes there are no limbs attached to the body. For in accordance with their essential constitution they are swimming animals; and nature never makes anything superfluous8 or void of use. Now inasmuch as fishes are made swimming they have fins, and as they are not made for walking they are without feet; for feet are attached to the body that they may be of use in progression on land. Moreover, fishes cannot have feet, or any other similar limbs, as well as four fins; for they are essentially9 sanguineous animals. The Cordylus, though it has gills, has feet, for it has no fins but merely has its tail flattened10 out and loose in texture11.
Fishes, unless, like the Batos and the Trygon, they are broad and flat, have four fins, two on the upper and two on the under side of the body; and no fish ever has more than these. For, if it had, it would be a bloodless animal.
The upper pair of fins is present in nearly all fishes, but not so the under pair; for these are wanting in some of those fishes that have long thick bodies, such as the eel12, the conger, and a certain kind of Cestreus that is found in the lake at Siphae. When the body is still more elongated, and resembles that of a serpent rather than that of a fish, as is the case in the Smuraena, there are absolutely no fins at all; and locomotion13 is effected by the flexures of the body, the water being put to the same use by these fishes as is the ground by serpents. For serpents swim in water exactly in the same way as they glide14 on the ground. The reason for these serpent-like fishes being without fins is the same as that which causes serpents to be without feet; and what this is has been already stated in the dissertations15 on the Progression and the Motion of Animals. The reason was this. If the points of motion were four, motion would be effected under difficulties; for either the two pairs of fins would be close to each other, in which case motion would scarcely be possible, or they would be at a very considerable distance apart, in which case the long interval16 between them would be just as great an evil. On the other hand, to have more than four such motor points would convert the fishes into bloodless animals. A similar explanation applies to the case of those fishes that have only two fins. For here again the body is of great length and like that of a serpent, and its undulations do the office of the two missing fins. It is owing to this that such fishes can even crawl on dry ground, and can live there for a considerable time; and do not begin to gasp17 until they have been for a considerable time out of the water, while others, whose nature is akin18 to that of land-animals, do not even do as much as that. In such fishes as have but two fins it is the upper pair (pectorals) that is present, excepting when the flat broad shape of the body prevents this. The fins in such cases are placed at the head, because in this region there is no elongation, which might serve in the absence of fins as a means of locomotion; whereas in the direction of the tail there is a considerable lengthening19 out in fishes of this conformation. As for the Bati and the like, they use the marginal part of their flattened bodies in place of fins for swimming.
In the Torpedo and the Fishing-frog the breadth of the anterior part of the body is not so great as to render locomotion by fins impossible, but in consequence of it the upper pair (pectorals) are placed further back and the under pair (ventrals) are placed close to the head, while to compensate20 for this advancement21 they are reduced in size so as to be smaller than the upper ones. In the Torpedo the two upper fins (pectorals) are placed on the tail, and the fish uses the broad expansion of its body to supply their place, each lateral22 half of its circumference23 serving the office of a fin3.
The head, with its several parts, as also the organs of sense, have already come under consideration.
There is one peculiarity24 which distinguishes fishes from all other sanguineous animals, namely, the possession of gills. Why they have these organs has been set forth25 in the treatise26 on Respiration27. These gills are in most fishes covered by opercula, but in the Selachia, owing to the skeleton being cartilaginous, there are no such coverings. For an operculum requires fish-spine28 for its formation, and in other fishes the skeleton is made of this substance, whereas in the Selachia it is invariably formed of cartilage. Again, while the motions of spinous fishes are rapid, those of the Selachia are sluggish29, inasmuch as they have neither fish-spine nor sinew; but an operculum requires rapidity of motion, seeing that the office of the gills is to minister as it were to expiration30. For this reason in Selachia the branchial orifices themselves effect their own closure, and thus there is no need for an operculum to ensure its taking place with due rapidity. In some fishes the gills are numerous, in others few in number; in some again they are double, in others single. The last gill in most cases is single. For a detailed31 account of all this, reference must be made to the treatises32 on Anatomy33, and to the book of Researches concerning Animals.
It is the abundance or the deficiency of the cardiac heat which determines the numerical abundance or deficiency of the gills. For, the greater an animal’s heat, the more rapid and the more forcible does it require the branchial movement to be; and numerous and double gills act with more force and rapidity than such as are few and single. Thus, too, it is that some fishes that have but few gills, and those of comparatively small efficacy, can live out of water for a considerable time; for in them there is no great demand for refrigeration. Such, for example, are the eel and all other fishes of serpent-like form.
Fishes also present diversities as regards the mouth. For in some this is placed in front, at the very extremity34 of the body, while in others, as the dolphin and the Selachia, it is placed on the under surface; so that these fishes turn on the back in order to take their food. The purpose of Nature in this was apparently35 not merely to provide a means of salvation36 for other animals, by allowing them opportunity of escape during the time lost in the act of turning-for all the fishes with this kind of mouth prey37 on living animals-but also to prevent these fishes from giving way too much to their gluttonous38 ravening39 after food. For had they been able to seize their prey more easily than they do, they would soon have perished from over-repletion. An additional reason is that the projecting extremity of the head in these fishes is round and small, and therefore cannot admit of a wide opening.
Again, even when the mouth is not placed on the under surface, there are differences in the extent to which it can open. For in some cases it can gape40 widely, while in others it is set at the point of a small tapering41 snout; the former being the case in carnivorous fishes, such as those with sharp interfitting teeth, whose strength lies in their mouth, while the latter is its form in all such as are not carnivorous.
The skin is in some fishes covered with scales (the scale of a fish is a thin and shiny film, and therefore easily becomes detached from the surface of the body). In others it is rough, as for instance in the Rhine, the Batos, and the like. Fewest of all are those whose skin is smooth. The Selachia have no scales, but a rough skin. This is explained by their cartilaginous skeleton. For the earthy material which has been thence diverted is expended42 by nature upon the skin.
No fish has testicles either externally or internally; as indeed have no apodous animals, among which of course are included the serpents. One and the same orifice serves both for the excrement43 and for the generative secretions44, as is the case also in all other oviparous animals, whether two-footed or four-footed, inasmuch as they have no urinary bladder and form no fluid excretion.
Such then are the characters which distinguish fishes from all other animals. But dolphins and whales and all such Cetacea are without gills; and, having a lung, are provided with a blow-hole; for this serves them to discharge the sea-water which has been taken into the mouth. For, feeding as they do in the water, they cannot but let this fluid enter into their mouth, and, having let it in, they must of necessity let it out again. The use of gills, however, as has been explained in the treatise on Respiration, is limited to such animals as do not breathe; for no animal can possibly possess gills and at the same time be a respiratory animal. In order, therefore, that these Cetacea may discharge the water, they are provided with a blow-hole. This is placed in front of the brain; for otherwise it would have cut off the brain from the spine. The reason for these animals having a lung and breathing, is that animals of large size require an excess of heat, to facilitate their motion. A lung, therefore, is placed within their body, and is fully45 supplied with blood-heat. These creatures are after a fashion land and water animals in one. For so far as they are inhalers of air they resemble land-animals, while they resemble water-animals in having no feet and in deriving46 their food from the sea. So also seals lie halfway47 between land and water animals, and bats half-way between animals that live on the ground and animals that fly; and so belong to both kinds or to neither. For seals, if looked on as water-animals, are yet found to have feet; and, if looked on as land-animals, are yet found to have fins. For their hind7 feet are exactly like the fins of fishes; and their teeth also are sharp and interfitting as in fishes. Bats again, if regarded as winged animals, have feet; and, if regarded as quadrupeds, are without them. So also they have neither the tail of a quadruped nor the tail of a bird; no quadruped’s tail, because they are winted animals; no bird’s tail, because they are terrestrial. This absence of tail is the result of necessity. For bats fly by means of a membrane48, but no animal, unless it has barbed feathers, has the tail of a bird; for a bird’s tail is composed of such feathers. As for a quadruped’s tail, it would be an actual impediment, if present among the feathers.
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1
stunting
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| v.阻碍…发育[生长]，抑制，妨碍( stunt的现在分词 ) | |
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2
fins
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| [医]散热片；鱼鳍；飞边；鸭掌 | |
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3
fin
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| n.鳍；(飞机的)安定翼 | |
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4
elongated
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| v.延长，加长( elongate的过去式和过去分词 ) | |
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5
torpedo
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| n.水雷，地雷；v.用鱼雷破坏 | |
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6
anterior
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| adj.较早的；在前的 | |
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7
hind
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| adj.后面的，后部的 | |
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8
superfluous
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| adj.过多的，过剩的，多余的 | |
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9
essentially
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| adv.本质上，实质上，基本上 | |
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10
flattened
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| [医]（水）平扁的，弄平的 | |
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11
texture
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| n.(织物)质地；(材料)构造；结构；肌理 | |
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12
eel
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| n.鳗鲡 | |
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locomotion
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| n.运动，移动 | |
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14
glide
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| n./v.溜，滑行；(时间)消逝 | |
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15
dissertations
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| 专题论文，学位论文( dissertation的名词复数 ) | |
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16
interval
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| n.间隔，间距；幕间休息，中场休息 | |
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17
gasp
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| n.喘息，气喘；v.喘息；气吁吁他说 | |
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18
akin
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| adj.同族的，类似的 | |
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19
lengthening
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| （时间或空间）延长，伸长( lengthen的现在分词 )； 加长 | |
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20
compensate
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| vt.补偿，赔偿；酬报 vi.弥补；补偿；抵消 | |
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21
advancement
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| n.前进，促进，提升 | |
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22
lateral
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| adj.侧面的，旁边的 | |
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23
circumference
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| n.圆周，周长，圆周线 | |
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24
peculiarity
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| n.独特性，特色；特殊的东西；怪癖 | |
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25
forth
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| adv.向前；向外，往外 | |
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26
treatise
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| n.专著；(专题)论文 | |
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27
respiration
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| n.呼吸作用；一次呼吸；植物光合作用 | |
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28
spine
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| n.脊柱，脊椎；(动植物的)刺；书脊 | |
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29
sluggish
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| adj.懒惰的，迟钝的，无精打采的 | |
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30
expiration
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| n.终结，期满，呼气，呼出物 | |
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31
detailed
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| adj.详细的，详尽的，极注意细节的，完全的 | |
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32
treatises
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| n.专题著作，专题论文，专著( treatise的名词复数 ) | |
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33
anatomy
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| n.解剖学，解剖；功能，结构，组织 | |
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34
extremity
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| n.末端，尽头；尽力；终极；极度 | |
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35
apparently
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| adv.显然地；表面上，似乎 | |
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36
salvation
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| n.（尤指基督）救世，超度，拯救，解困 | |
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37
prey
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| n.被掠食者，牺牲者，掠食；v.捕食，掠夺，折磨 | |
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38
gluttonous
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| adj.贪吃的，贪婪的 | |
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39
ravening
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| a.贪婪而饥饿的 | |
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40
gape
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| v.张口，打呵欠，目瞪口呆地凝视 | |
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41
tapering
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| adj.尖端细的 | |
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42
expended
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| v.花费( expend的过去式和过去分词 )；使用（钱等）做某事；用光；耗尽 | |
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43
excrement
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| n.排泄物，粪便 | |
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44
secretions
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| n.分泌（物）( secretion的名词复数 ) | |
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45
fully
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| adv.完全地，全部地，彻底地；充分地 | |
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46
deriving
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| v.得到( derive的现在分词 )；（从…中）得到获得；源于；（从…中）提取 | |
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47
halfway
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| adj.中途的，不彻底的，部分的；adv.半路地，在中途，在半途 | |
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48
membrane
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| n.薄膜，膜皮，羊皮纸 | |
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