GENERATION OF ANIMALS, III. n. 



|of the fetation is complete, the whole egg is released, 

 and, as we should expect, nothing is to be seen of the 

 umbilical cord, because it is the tip of the extreme 

 end of the egg. 



Eggs and the young of viviparous animals come out 

 facing opposite ways ; the latter come out with the 

 head and the " principle " first '^ ; the egg comes out 

 as it were feet first. And the reason I have stated : 

 it is because the egg is fastened at the point where 

 the " principle "is. 



The formation of birds out of the egg is effected by incubation, 

 the mother's sitting on the eggs and helping to 

 concoct them. One part of the egg yields the sub- 

 stance out of which the animal is constituted, the 

 remaining part proxides the substance whereby it 

 grows and is perfected ; Nature puts both in the egg 

 — the material for making the animal, and sufficient 

 nourishment for its growth,'' since the hen cannot 

 bring the young to perfection within herself, and 

 therefore M'hen she lays an egg she lays the creature's 

 nourishment in it as well. The nourishment for the 

 young of viviparous animals, what we call milk, is 

 formed in the breasts, a different part of the body 

 altogether ; but for birds Nature pro\ides this inside 

 their eggs. The truth about it, however, is the 

 reverse of what is commonly supposed and what is 

 asserted by Alcmeon of Crotona."^ It is not the white 

 of the egg that is the milk, but the yolk, because it 

 is the yolk that is the nourishment for the chicks. 

 These people suppose that the white is, owing to 

 the similarity of colour. ** 



The formation of the chick, then, as I have said, is 

 effected by the mother-bird's sitting upon the egg ; 

 notNsithstanding, if the cHmate is well-tempered or 



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