310 FORMATION OF THE EGG AND CHICKEN 
pronounced specializations are the definite formation of body walls 
and a rudimentary growth of feathers. At this period the white 
or albumin has practically disappeared. The beak is formed, and 
gives the embryo a distinctly birdlike appearance. The head is 
proportionately large, and the eyes extremely so. The body is 
‘very bulky, owing to the large size of the heart and liver. The 
legs have increased greatly in size, and the division of the extrem- 
ities into toes*is very marked. The yolk sac, while yet large, is 
very flabby, from the absorption of nutriment. 
The feathers may be distinctly seen on the ninth day. They 
are enclosed in a small sac, in which they grow to about one- 
quarter of an inch in length before hatching time, but the sac is 
not broken until then. By the thirteenth day the beak and nails 
have taken on a hard, horny appearance. 
Motion can be discerned in the embryo on about the sixth day, 
but it is very slight, and there is no pronounced movement of the 
entire embryo until the fourteenth day. Up to this latter time the 
chick has been lying with its body at right angles to the long axis 
of the egg. Now it turns, so that the body lies lengthwise of the 
egg, the beak in contact with the inner membrane of the shell 
about one-quarter of the way from the large end of the egg. The 
air cell is now much enlarged, owing to evaporation of the fluids, 
and the additional space so formed is utilized by the chick at 
hatching. Infrequent turning of the eggs, or weakness of the 
embryo, will not permit the change of position on the fourteenth 
day; there will be what is termed a ‘“‘false presentation,”’ and, in the 
majority of cases, the chick will not be able to get out of the shell. 
By the twentieth day the embryo will have grown so that it 
occupies all of the egg except the air cell, the yolk will have been 
nearly all absorbed, and what remains is drawn into the body 
at the umbilicus (navel opening), the body walls closing over 
the opening. This process of absorption is an important factor 
in the early life of the chick, since it is the source of nourishment 
until the chick can digest and assimilate feed from outside sources. 
Process of Hatching.—The process of hatching is one of the 
most striking phenomena connected with the development of the 
young chick, and is interesting alike to the experienced and in- 
experienced. The process is approximately as follows: 
When ready to leave the shell, which is usually on the twentieth 
or twenty-first day, the chick tears the inner shell membrane with 
its beak, stretches its neck, and, occupying the extra air space, at 
once begins to breathe the air which it contained. As a result of 
