THE INCUBATION OF THE EGG 215 



In making a study of the effect of crowding eggs into the 

 trays for the purpose of increasing the capacity of the 

 incubator, Jackson^ reached the conclusion that in the case 

 of white eggs, which could be tested for fertility after three 

 days of incubation, crowding so that the eggs stand on end 

 until the first test results in no serious disadvantage. 



Turning Eggs. — ^The hen turns the eggs she is incubating 

 in two ways. The first is by peculiar lateral movements of 

 the body with which she settles on the nest after feeding, 

 and which she continues from time to time throughout the 

 day and probably throughout the night. The purpose of 

 these lateral movements is presumably to seek a more 

 comfortable position. The practical results are to bring 

 the body in closer contact with the egg and so closer to the 

 developing germ, and also to turn the egg. The second way 

 is by what is incorrectly called "billing," in which the hen 

 reaches under her body and rearranges the eggs with her 

 beak. She is particularly likely to do this if there are more 

 eggs in the nest than she can properly cover. She frequently 

 pushes the eggs back under cover. 



Such observations as have been reported show that in 

 artificial incubation fairly frequent turnings increase the 

 hatching power of eggs. Eycleshymer^ found that where 

 eggs were unmoved during the incubation period but 15 per 

 cent, of fertile eggs hatched. A very large proportion of the 

 fertile eggs that failed to hatch did so because in the early 

 stages the embryo, or in the later stages the allantois, had 

 adhered to the shell. It is assumed that this could have been 

 largely overcome by turning. 



Eggs from the same hens that were turned at 6 a.m. and 

 6 P.M. gave a hatch of 58 per cent, of fertile eggs. In this 

 same connection, Jackson^ kept a record of 1350 eggs, half 

 of which were turned twice daily during the incubation 

 period, while the remainder were unturned. These eggs 

 were distributed in equal lots through several different 

 incubators. Although the group of eggs that were turned 

 twice daily contained six more infertile eggs than the other 



1 Pennsylvania Bulletin No. 120. 



' Biological Bulletin, May, 1907. ' Pennsylvania Bulletin No. 120. 



