PERIOD OF INCUBATION 



321 



Period of Incubation. The hen's 

 egg requires approximately twenty- 

 one days for incubation. This pe- 

 riod, however, varies considerably in 

 eggs from different breeds; for in- 

 stance, the white-shelled eggs of the 

 Leghorns, under uniform conditions, 

 will pip and a great many hatch on 

 the twentieth day, while under 

 the same circumstances the Brahma 

 eggs will take at least twenty-two 

 days. This is probably due to quick- 

 er development of the germ of the 

 Leghorns and to the fact that the 

 eggshell is thinner. The periods of 

 incubation required for other birds 

 are: Ducks, twenty-eight days; 

 swans, from thirty-two to thirty- 

 five, usually thirty-five days ; geese, 

 thirty to thirty-five days; turkeys, 

 peafowls, and guineas, twenty-eight 

 days. These are the average natu- 

 ral incubation periods; in artificial 

 incubation the time varies some- 

 what. They may also be affected 

 by the degree of heat which the 

 broody hen develops. The closer 

 she sits and the greater heat she 

 generates, the shorter will be the 

 incubation period. Chicks which 

 hatch much in advance of the nor- 

 mal period or exceedingly late are 

 of no value, for this indicates low 

 vitality. The best chicks are those 

 which are hatched at a uniform time, 

 the great majority breaking the shell 

 on or about the times mentioned. 

 A severe chilling of the eggs during 

 incubation will of ten kill the embryo, 

 or at least retard the hatch from 

 twenty-four to forty-eight hours. 

 21 



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FlG 15 2._ M niier of toe punching 

 for baby chicks, showing sixteen com- 



binations, making it possible to identify 



sixteen different 



