THE INCUBATION OF HENS' EGGS 101 



males in the long run give about 50 per cent females, and 

 that the short, round eggs supposed to produce a preponder- 

 ance of females, when hatched in large numbers produce a 

 little above or below 50 per cent of males. 



The position of the air cell during incubation, though not so 

 widely preached, is eciually unreliable as a means of pre- 

 judging sex. It has been maintained that when tlie air cell 

 develops so that the long axis of the egg passes through the 

 approximate center of the air space the sex of the developing 

 embryo is male. When the long axis is very much eccentric 

 and the cell extends down the side of the egg the sex of the 

 embryo is said to be female. The author had occasion to 

 examine sc\eral lunidred eggs for the ])iu'pose of observing 

 the relative numbers of each sex hatched from eggs containing 

 each type of air cell. Unfortunately the detailed data have 

 not been preserved, but the sex of the resulting chicks in 

 each case was represented in ncarl^y equal numbers. 



The only means of predetermining the fertility of an 

 egg that has had any very general acceptance has been by 

 determining the relative specific gravity of eggs. 



The claim is made that the eggs showing a great specific 

 gravity are fertile, while those whose specific gravity is 

 much less are infertile. As a matter of fact, these ditt'erences 

 between the eggs of certain hens may be observed whether 

 the hens have \>een mated with males and are laying eggs 

 that are presumably fertile, or whether they have been 

 separated from male birds for several weeks. While there 

 does appear to be a correlation between the specific gravity 

 of an egg and the vigor of the hen laying it on the one hand, 

 and the chick hatching from it on the other, there is no notice- 

 able correlation between the fact of a great specific gravity 

 and the fact of fertilization. 



Care of Hatching Eggs. — At the time the fertile egg is laid 

 it is usually in a fairly advanced stage of development from 

 an embryological stand-point, having been inculcated within 

 the body of the hen for approximately twenty-four hours. 

 It would seem that the ideal method of caring for hatching 

 eggs would be to allow development to proceed without 

 checking, by incubating the eggs at once without ever 



