534 PLlrfs NATUEAL HISTORY. Book X. 



blackbirds, ring-doves, and turtle-doves sit twice a year, most 

 other birds only once. Thrushes make their nests of mud, in 

 the tops of trees, almost touching one another, and lay during 

 the time of their retirement. The egg comes to maturity in the 

 ovary ten days after treading ; but if the hen or pigeon is tor- 

 mented by pulling out the feathers, or by the infliction of any 

 injury of a similar nature, the maturing of the egg is retarded. 

 In the middle of the yolk of every egg there is what ap- 

 pears to be a little drop^^ of blood; this is supposed to be 

 the heart of the chicken, it being the general belief that that 

 part is formed the first in every animal : at all events, while 

 in the egg this speck is seen to throb and palpitate. The body 

 of the animal itself is formed from the white fluid ^" in the 

 egg ; while the yellow part constitutes its food. The head in 

 every kind, while in the shell, is larger than the rest of the 

 body ; the eyes, too, are closed, and are larger than the other 

 parts of the head. As the chicken grows, the white gradually 

 passes to the middle of the egg, while the yellow is spread 

 around it. On the twentieth day, if the egg is shaken, the 

 voice of the now living animal can be heard in the shell. From 

 this time it gradually becomes clothed with feathers ; and its 

 position is such that it has the head above the right foot, and 

 the right wing above the head : the yolk in the meantime 

 gradually disappears. All birds are born with the feet first, 

 while with every other animal the contrary is the case. Some 

 hens lay all their eggs with two yolks, and sometimes hatch 

 twin chickens from the same egg, one being larger than the 

 other, according to Cornelius Celsus : other writers, however, 

 deny^^ the possibility of twin chickens being hatched. It is 

 a rule never to give a brood hen more than twenty-five^^ eggs 

 to sit upon at once. Hens begin to lay immediately after the 

 winter solstice. The best broods are those which are hatched 



^9 Cuvier says, that after an egg has been set upon for some days, the 

 heart of the chicken may be seen like a small red speck, that palpitates ; 

 but that no such thing is to he seen before incubation. 



20 Cuvier remarks, that the chicken is not formed exclusively from the 

 white, and that the yellow is gradually displaced by it, as the chicken in- 

 creases in size. 



-1 Cuvier tells us, that in the Memoirs of the Academy of St. Petersburgh, 

 there is a memoir by Wolf, entitled Ovum simplex gemelliferum, in which 

 these twin chickens are described with ^reat exactness. 



22 More generally eleven or thirteen in this country. 



