by Aristotle
[30] The second umbilical cord runs to the surrounding chorion. For we must understand that, in the case of animals developed in eggs, they have the same relation to the yolk as the embryo of the vivipara has to the mother so long as it is within the mother (for since the nourishment of the embryo of the ovipara is not completed within the mother, the embryo takes part of it away from her); and their relation to the outermost membrane, the sanguineous one, is like that of the viviparous embryo to the uterus. At the same time the egg-shell surrounds both the [754a1] yolk and the chorion analogous to the uterus, just as if it should be put round both the embryo itself and the whole of the mother. This is so because the embryo must [5] be in the uterus and attached to the mother. Now in the vivipara the uterus is within the mother, but in the ovipara it is the other way about, as if one should say that the mother was in the uterus, for that which comes from the mother, the nutriment, is the yolk. The reason is that the process of nourishment is not completed within the mother.
[10] As the creature grows the umbilicus running to the chorion collapses first, because it is here that the young is to come out; what is left of the yolk, and the umbilical cord running to the yolk, collapse later. For the young must have nourishment as soon as it is hatched; it is not nursed by the mother and cannot immediately procure its nourishment for itself; therefore the yolk enters within it [15] along with its umbilicus and the flesh grows round it.
This then is the manner in which animals produced from perfect eggs are hatched in all those, whether birds or quadrupeds, which lay eggs with a hard shell. These details are plainer in the larger creatures; in the smaller they are obscure [20] because of the smallness of the masses concerned.
3 · The class of fishes is also oviparous. Those among them which have the uterus low down lay an imperfect egg for the reason previously given, but the so-called Selachia produce a perfect egg within themselves but are externally [25] viviparous except one which they call the fishing-frog; this alone lays a perfect egg externally. The reason is the nature of its body, for its head is many times as large as the rest of the body and is spiny and very rough. This is also why it does not receive its young again within itself nor produce them alive to begin with, for as the size and [30] roughness of the head prevents their entering so it would prevent their exit. And while the egg of the Selachia is soft-shelled (for they cannot harden and dry its circumference, being colder than birds), the egg of the fishing-frog alone is solid and firm to protect it outside, but those of the rest are of a moist and soft nature, for [754b1] they are sheltered within and by the body of the mother.
The young are produced from the egg in the same way both with those externally perfected (the fishing-frogs) and those internally, and the process in these eggs is partly similar to, partly different from that in birds’ eggs. In the first place they have not the second umbilicus which runs to the chorion under the [5] surrounding shell. The reason of this is that they have not the surrounding shell, for it is no use to them since the mother shelters them, and the shell is a protection to the laid eggs against external injury. Secondly, the process in these also begins on the surface of the egg but not where it is attached to the uterus; for birds are [10] developed from the sharp end and that is where the egg was attached. The reason is that the egg of birds is separated from the uterus, but in most though not all Selachia the egg is still attached to the uterus when perfect. While the young develops upon the surface the egg is consumed by it just as in birds and the other [15] animals detached from the uterus, and at last the umbilicus of the now perfect fish is left attached to the uterus. The like is the case with all those whose eggs are detached from the uterus, for in some of them the egg is so detached when it is perfect.
The question may be raised why the development of birds and fishes differs in [20] this respect. The reason is that in birds the white and yolk are separate, but fish eggs are one-coloured, the corresponding matter being completely mixed, so that there is nothing to stop the first principle being at the opposite end, for the egg is of the same nature both at the point of attachment and at the opposite end, and it is easy to draw [25] the nourishment from the uterus by passages running from this principle. This is plain in the eggs which are not detached, for in some of the Selachia the egg is not detached from the uterus, but is still connected with it as it comes downwards with a view to the production of the young alive; in these the young fish when perfected is [30] still connected by the umbilicus to the uterus when the egg has been consumed. From this it is clear that previously also, while the egg was still round the young, the passages ran to the uterus. This happens as we have said in the smooth dogfish.
In these respects and for the reasons given, the development of fishes differs from that of birds, but otherwise it takes place in the same way. For they have the one umbilicus in like manner as that of birds connecting with the yolk—only in [755a1] these fishes it connects with the whole egg (for it is not divided into white and yolk but all one-coloured)—and get their nourishment from this, and as it is being consumed the flesh in like manner encroaches upon and grows round it. [5]
Such is the process of development in those fish that produce a perfect egg within themselves but are externally viviparous.
4 · Most of the other fish are externally oviparous, all laying an imperfect egg except the fishing-frog; the reason for this exception has been previously stated, and the reason also why the others lay imperfect eggs. In these also the development [10] from the egg runs on the same lines as that of the Selachian and internally oviparous fishes, except that the growth is quick and from small beginnings and the outside of the egg is harder. The growth of the egg is like that of a grub, for those animals which produce grubs give birth to a small thing at first and this grows by itself and [15] not through any attachment to the parent. The reason is similar to that of the growth of yeast, for yeast also grows great from a small beginning as the more solid part liquefies and the liquid is aerated. This is effected in animals by the nature of [20] the vital heat, in yeasts by the heat of the juice commingled with them. The eggs then grow of necessity through this cause (for they have in them a yeasty residue), but also for the sake of what is better; for it is impossible for them to attain their [25] whole growth in the uterus because these animals have so many eggs. Therefore they are very small when set free and grow quickly, small because the uterus is narrow for the multitude of the eggs, and growing quickly that the race may not perish, as it would if much of the time required for the whole development were [30] spent in this growth; even as it is most of those laid are destroyed. Hence the class of fish is prolific, for nature makes up for the destruction by numbers. Some fish actually burst because of the size of the eggs, as the fish called the pipe-fish—for its eggs are large instead of numerous, what nature has taken away in number being [35] added in size.
So much for the growth of such eggs and its reason.
[755b1] 5 · A proof that these fish also are oviparous is the fact that even viviparous fish, such as the Selachia, are first internally oviparous, for it is plain that the whole class of fishes is oviparous. Where, however, both sexes exist and the eggs are [5] produced in consequence of impregnation, the eggs do not arrive at completion unless the male sprinkle his milt upon them. Some erroneously assert that all fish are female except in the Selachian fishes, for they think that the females of fish differ from what are supposed to be males only in the same way as in those plants [10] where the one bears fruit but the other is fruitless, as olive and oleaster, fig and caprifig. They think the like applies to fish except the Selachia; for they do not dispute the sexes in these. And yet there is no difference in the males of Selachian fishes and those belonging to the oviparous class in respect of the organs for the [15] milt, and semen can be seen oozing out of males of both classes at the right season. The female also has a uterus. But if the whole class were females and some of them unproductive, then not only should those which lay eggs have a uterus but also the others, only
the uterus of the latter should be different from that of the former. But, [20] as it is, some of them have organs for milt and others have a uterus, and this distinction obtains in all except two, the erythrinus and the channa, some of them having the milt organs, others a uterus. The difficulty which drives some thinkers to this conclusion is easily solved if we look at the facts. They say quite correctly that [25] no animal which copulates produces many young, for of all those that generate from themselves perfect animals or perfect eggs none is prolific on the same scale as the oviparous fishes, for the number of eggs in these is enormous. But they had overlooked the fact that fish-eggs differ from those of birds in one circumstance. [30] Birds and all oviparous quadrupeds, and any of the Selachia that are oviparous, produce a perfect egg, and it does not increase outside of them, whereas the eggs of fish are imperfect and do so complete their growth. Moreover the same thing applies to cephalopods also and crustacea, yet these animals are actually seen [35] copulating, for their union lasts a long time, and it is plain in these cases that the one is male and the other has a uterus. Finally, it would be strange if this distinction did [756a1] not exist in the whole class, just as male and female in all the vivipara. The cause of the ignorance of those who make this statement is that the differences in the copulation and generation of various animals are of all kinds and not obvious, and so, basing their study on a few cases, they think the same must hold good in all cases. [5]
So also those who assert that conception in female fishes is caused by their swallowing the semen have not observed certain points when they say this. For the males have their milt and the females their eggs at about the same time of year, and the nearer the female is to laying the more abundant and the more liquid is the milt [10] formed in the male. And just as the increase of the milt in the male and of the egg in the female takes place at the same time, so is it also with their emission, for neither do the females lay all their eggs together, but gradually, nor do the males emit all the milt at once. All these facts are in accordance with reason. For just as the class [15] of birds in some cases has eggs without impregnation, but few and seldom, impregnation being generally required, so we find the same thing, though to a less degree, in fish. But in both classes these spontaneous eggs are infertile unless the male, in those kinds where the male exists, shed his fluid upon them. Now in birds [20] this must take place while the eggs are still within the mother, because they are perfect when discharged, but in fish, because the eggs are imperfect and complete their growth outside the mother in all cases, those outside are preserved by the sprinkling of the milt over them, even if nothing fertile comes into being inside by way of impregnation, and here it is that the milt of the males is used up. Therefore it [25] comes down the ducts and diminishes in quantity at the same time as this happens to the eggs of the females, for the males always attend them, shedding their milt upon the eggs as they are laid. Thus then they are male and female, and all of them copulate (unless in any kind the distinction of sex does not exist), and without the semen of the male no such animal comes into being. [30]
What contributes to their error is also the fact that the union of such fishes is brief, so that it is not observed even by many of the fishermen, for none of them ever watches anything of the sort for the sake of knowledge. Nevertheless their copulation has been seen, for fish (when the tail part does not prevent it)6 copulate like the dolphins by throwing themselves alongside of one another. But the dolphins [756b1] take longer to get free again, whereas such fishes do so quickly. Hence, not seeing this, but seeing the swallowing of the milt and the eggs, even the fishermen repeat [5] the same simple tale, so much noised abroad, as does Herodotus the story-teller,7 as if fish were conceived by the mother’s swallowing the milt—not considering that this is impossible. For the passage which enters by way of the mouth runs to the intestines, not to the uterus, and what goes into the intestines must be turned into [10] nutriment, for it is concocted; the uterus, however, is plainly full of eggs, and from whence did they enter it?
6 · A similar story is told also of the generation of birds. For there are some who say that the raven and the ibis unite at the mouth, and among quadrupeds that [15] the weasel brings forth its young by the mouth; so say Anaxagoras and some of the other natural scientists, speaking too superficially and without consideration. Concerning the birds, they are deceived by a false reasoning, because the copulation [20] of ravens is seldom seen, but they are often seen uniting with one another with their beaks, as do all the birds of the raven family; this is plain with domesticated jackdaws. Birds of the pigeon kind do the same, but, because they also plainly copulate, therefore they have not had the same legend told of them. But the raven [25] family is not amorous, for they are birds that produce few young, though this bird also has been seen copulating before now. It is a strange thing, however, that these theorists do not ask themselves how the semen enters the uterus through the intestine, which always concocts whatever comes into it, as the nutriment; and these [30] birds have a uterus like others, and eggs are found in them near the hypozoma. And the weasel has a uterus in like manner to the other quadrupeds; by what passage is the embryo to get from it to the mouth? But this opinion has arisen because the young of the weasel are very small like those of the other fissipeds, of which we shall [757a1] speak later, and because they often carry the young about in their mouths.
Much deceived also are those who make a foolish statement about the trochus and the hyena. Many say that the hyena, and Herodorus of Heraclea says that the [5] trochus, has two pudenda, those of the male and of the female, and that the trochus impregnates itself but the hyena mounts and is mounted in alternate years. This is untrue, for the hyena has been seen to have only one pudendum, there being no lack of opportunity for observation in some districts, but hyenas have under the tail a line [10] like the pudendum of the female. Both male and female have such a mark, but the males are taken more frequently; this casual observation has given rise to this opinion. But enough has been said of this.
7 · Touching the generation of fish, the question may be raised, why it is that [15] in the selachia neither the females are seen discharging their eggs nor the males their milt, whereas in the non-viviparous fishes this is seen in both sexes. The reason is that the whole selachian class do not produce much semen, and further the females have their uterus near the hypozoma. For the males and females of the one [20] class of fish differ from the males and females of the other class in like manner, for the selachia are less productive of semen. But in the oviparous fish, as the females lay their eggs on account of their number, so do the males shed their milt on account of its abundance. For they have more milt than just what is required for copulation, [25] as nature prefers to expend the milt in helping to perfect the eggs, when the female has deposited them, rather than in forming them at first. For as has been said both further back and in our recent discussions, the eggs of birds are perfected internally but those of fish externally. The latter, indeed, resemble in a way those animals [30] which produce a grub; for the product discharged by them is still more imperfect. It is the male that brings about the perfection of the egg both of birds and of fishes, only in the former internally, as they are perfected internally, and in the latter externally, because the egg is imperfect when deposited; but the result is the same in both cases.
[757b1] In birds the wind-eggs become fertile, and those previously impregnated by one kind of male change their nature to that of the later impregnator. And if the eggs be behindhand in growth, then, if the same cock treads the hen again after leaving off treading for a time,8 he causes them to increase quickly, not, however, at [5] any period whatever, but if the treading take place before the egg changes so far that the white begins to separate from the yolk. But in the eggs of fishes no such limit of time has been laid down, but the males shed their milt quickly upon them to preserve them. The reason is that these eggs are not two-coloured, and hence there is no such limit of time fixed with them as with those of birds
. This fact is what we [10] should expect, for by the time that the white and yolk are separated off from one another, the bird’s egg already contains the principle that comes from the male parent (for the male contributes this).