THE INCVBATION OF HENS' EGGS 



1S5 



more rapidly and to assume a more proptirtionate size. About 

 the tenth da.y 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 oi)ening, 

 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. 



Fig. 00 



Embryo chick, fijrty-eiglit hours ohi, with the Ijeart located outside the 

 body, IMagnified. (Courtesy of Iowa 7\^riciibural Experirnont Station.) 



By the thirteenth day the feathers are distributed over the 

 body. Their color may be seen through the thin walls of the 

 sacs, which inclose them until the nineteenth day. On the 

 thirteenth day the scales and nails appear, and by the 

 sixteenth day are found to be quite firm and horny, as is 

 also the beak. By the sixteenth day the white of the egg 

 has disappeared, and the embryo subsists thereafter wholly 



