534 
plint's katural 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 
19 Cuvier says, that after an egg has been set upon for some days, the 
heart of the chicken may be s.een hke a small red speck, that palpitates ; 
but that no such thing is to be seen before incubation. 
20 Cuvier remarks, that the chicken is not formed exclusively from the 
white, and that the yeUow is gradually displaced by it, as the chicken in- 
creases in size. 
21 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 great exactness. 
22 More generally eleven or thirteen in this country. 
