BOOK X. Lxx-iv. 145-149 



the rest a coek. The iiavel in eggs is at the top end, 

 projecting like a speck in the shell. 



Some birds mate in any season, for instance the Peri.iiiiyoj 

 domestic fowl, and lay, except in the two midwinter Modesoj 

 months. Of these kinds the young hens lay more ^^H^f^nq'^ 

 eggs than the old, but smaller ones, and in the same Physioioqn 

 brood those laid first and last are the smallest. But ^" ^^^' 

 they are so fertile that some even lay eggs sixty 

 times, some lay daily, some twice daily, some so 

 much that they die of exhaustion. Adria "■ birds 

 are most highly spoken of. Pigeons lay ten times 

 a year, some even eleven times, while in Egypt 

 they even lay in a midwinter month. Swallows and 

 blackbirds and woodpigeons and turtle-doves lay twice 

 a year, all other birds as a rule only once. Thrushes 

 build their nests of mud in an almost continuous 

 mass on the tops of trees, and breed in retirement. 

 The eggs grow to full size in the uterus in ten days 

 from pairing, but in the case of the domestic fowl 

 and the pigeon, if the hen is disturbed by having a 

 feather torn out or by some similar damage, it takes 

 longer. In all eggs the middle of the yolk contains a 

 small drop of a sort of blood, which people think is the 

 heart of birds, supposing that the heart is the first 

 part that is produced in every body : in an egg 

 undoubtedly this drop beats and throbs. The animal 

 itself is formed out of the white of the Qgg, but its 

 food is in the yolk.* In all cases at the beginning 

 the head is larger than the whole body, aud the eyes, 

 which are pressed together, are larger than the head. 

 As the chick grows in size the white turns to the 

 middle and the yolk spreads round it. If on the 

 twentieth day the egg be moved, the voice of the 



* Actually it is both the yolk and the white. 



387 



