THE INCUBATION OF THE EGG 



171 



the chick commences to pip the shell and the lungs and 

 kidneys of the chick commence to function. 



It is the veins of this allantois which are seen radiating 

 from the embryo at the first testing, about the seventh day 

 of incubation, and which may be noted plainly at the second 

 testing, about the fourteenth day. As soon as the chick 

 pips the shell, pulmonary circulation starts and the allantois 

 ceases to function, begins to degenerate, and is left behind 

 in the shell when the chick hatches. 



Fig. 83 



Appearance of a chick embryo after thirty-six hours in an incubator. 

 (Courtesy of Kansas Experiment Station.) 



Up to the sixth or seventh day there is nothing about the 

 chick embryo that would help one to distinguish it from the 

 embryo of any other animal. At this time the legs and wings 

 begin to take a recognizable form. The body, which has 

 been very small in proportion to the head, begins to develop 

 more rapidly and to assume a more proportionate size. About 

 the tenth day the little sacs containing the feathers begin to 

 protrude, particularly along the back of the embryo. At 

 this time there is a chalky deposit about the mouth opening, 

 which is the beginning of the horny beak. Upon breaking an 

 egg, what appears to be voluntary movement may be noticed 

 as early as the sixth day. 



