322 



VERTEBRATE ZOOLOGY 



day and are at first mere papillae protruding from the skin. At 

 hatching the chick is completely covered with down-feathers, which 

 are the forerunners of the definitive feathers and gradually give place 



FIG. 166. Chick embryo at 10 days and 2 hours, showing differentiated wing 

 and legs, shortened tail and feather papillse. (From Lillie, after Keibel and 

 Abraham.) 



to the latter. On about the seventeenth day the amniotic fluid begins 

 to disappear and on the twentieth day it is gone. On the same day 

 the chick, by means of a sharp little egg-tooth on the point of the bill, 

 pecks a hole in the shell and begins to breathe with its lungs. The 



