168 



POULTRY PRODUCTION 



sixteen hours after fertilization, which usually finds the egg 

 still within the body of the hen (Fig. 80). 



If, after laying, the temperature of a fertile egg is allowed 

 to fall below a temperature of 68° F., all growth ceases, and 

 the egg remains in a dormant condition until its temperature 

 is again raised to incubating temperatures. While develop- 

 ment takes place at all degrees of temperature between 



Fig. 80 



Embryo chick, sixteen hours old. Magnified. 

 Experiment Station.) 



(Courtesy of Iowa 



68° F. and that which is sufficiently high to destroy the life 

 of the egg, normal development only takes place at normal 

 temperatures. Pennington and Pierce^ note that at 86° F. 

 to 91° F. seven or eight days are required to equal three 

 days at the normal heat of incubation. The reverse, however, 



' Year-book, United States Department of Agriculture, 1910. 



