GENERATIatION of animals, III. VII. 



1 have now sa^-^^d-eggs become fertile," and e- 

 With regard to t^npf^rl bv t>»»^ vix-iJix^rc.rJ'^K/zle VII 

 may be raised, what the Cause can possibly be why I^^°s.^ 

 neither the females of Selachian fishes are seen 

 shedding their fetations nor the males their milt, 

 whereas the males and females are observed so doing 

 in the case of non-viviparous fishes. The reason is 

 that in general the class of the Selachians is not rich 

 in semen : and also in the females the uterus is up 

 towards the diaphragm." Of course males of one class 

 differ from males of another, and females similarly ; 

 and the fact is that the Selachians yield less semen 

 than most. With the oviparous fishes, the males 

 shed their milt, just as the females lay their eggs, 

 because there is such an abundance of both ; the 

 males have more milt than the amount which suffices 

 for copulation, because Nature prefers to expend the 

 milt in helping to enlarge the eggs after the female 

 has laid them, rather than in constituting the eggs 

 at the outset. This remark is explained by what has 

 been said both in our earlier discussion and also not 

 long ago, viz., the eggs of birds are perfected inside 

 the parent, but the eggs of fish outside. In a way, 

 fish resemble the larva-producing animals, for the 

 latter deposit a fetation which is even more imperfect 

 still. The perfecting in both cases, birds' eggs and 

 fishes', is accomplished by the male. With birds this 

 is done within the parent animal, because a bird's 

 egg is perfected inside ; vriih fishes, outside, because 

 the egg is in an imperfect state when it is deposited 

 outside. The upshot however is the same in both 

 cases. 



" And therefore the eggs are brought to perfection inside 

 the parent. 



519 



