2O 



OUR DOMESTIC BIRDS 



of its own kind or of some other kind, or to know whether the 

 young when hatched are like or unlike itself. If eggs fail to 

 hatch, domestic birds will, as a rule, remain on the nest until the 



FIG. 4. Fresh egg l 



FIG. 5. Infertile egg (after twenty- 

 four hours' incubation) 



FIG. 6. Fertile egg (after twenty- 

 four hours' incubation) 



FIG. 7. Embryo (after seventy-two 

 hours' incubation) 



eggs are taken away or until sheer exhaustion compels them to 

 abandon the hopeless task. In domestication, however, those 

 birds which continue laying most freely when their eggs are re- 

 moved as laid, tend to lose the habit of incubation. Turkeys and 



1 Photographs (Figs. 4-8) from Bureau of Animal Industry, United States Depart- 

 ment of Agriculture. 



