GENERATION OF ANIMALS, III. ii.-iii. 



it is the other way round — the mother is in the uterus, 

 as you might say, because in this case that which 

 comes from the mother [the nourishment] is the yolk. 

 The reason is that the embryo's period of nourishment 

 does not reach completion within the mother. 



As the embryos grow, the first of the umbilical 

 cords to collapse is the one which connects to the 

 chorion, because that is the point at which the young 

 animal v,i\\ have to make its way out ; the rest of the 

 volk and the cord which connects to it collapse later, 

 because the young animal must have nourishment 

 immediately it is hatched, as it is neither nursed by 

 its mother nor able immediately to get nourishment 

 by means of itself. That is why the yolk goes 

 inside it together with the umbilical cord and the 

 flesh grows round it. 



Such is the manner in which animals which are 

 brought to birth out of perfect eggs are produced in 

 the case of those birds and fishes which lay a hard- 

 shelled egg. The points mentioned are to be seen 

 more clearly in the larger animals ; in the smaller 

 ones they are not so obvious owing to the small bulk 

 of the animals. 



Another member of the Ovipara is the tribe of III 



fishes. (ii.) Fishes: 



Those fishes whose uterus is low dovvTi lay an imper- 

 fect egg. The cause of this I have stated prexiously." 

 The Selachian fishes as they are called produce a (a) Seiachia 

 perfect egg internally though they are externally 

 viviparous, except for one which they call the fishing- 

 frog ^ ; this is the only one that lays a perfect egg 

 externally. The cause of this is the nature of its 

 body. Its head is several times as large as the rest 

 of its body, and, besides that, spiny and extremely 



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