94 POULTRY PRODUCTION 



way dissolves some of the denser albumen already present, 

 and so brings about the dilution of the latter in some degree. 

 At the same time by this process of diffusion, the fluid layer 

 is rendered more dense, coming finally to the consistency of 

 the thin layer of the laid egg. The thin albumen layer, how- 

 ever, does not owe its existence in any sense to this dilution 

 factor, but to a definite secretion of a thin albumen by the 

 glands of the isthmus and uterus. The addition of albumen 

 to the egg is completed only after it has been in the uterus 

 from five to seven hours. 



"Before the acquisition of albumen by the egg is completed 

 a fairly considerable amount of shell substance has been 

 deposited on the shell membranes. For the completion of the 

 shell and the laying of the egg from twelve to sixteen, or 

 exceptionally even more, hours are required."' 



Curtis'* has shown that the larger an egg, the greater is 

 the mechanical stimulation upon the uterus and the heavier is 

 the shell. 



Infertile Eggs. — ^The discharging of the yolk or ovum from 

 the ovary of the hen is analogous to ovulation in other farm 

 animals. 



With the larger animals, if ovulation is not followed by 

 mating, there is no further development. With birds, 

 however, whether the ovum is fertilized in the funnel of the 

 oviduct by union with the male element or not, its further 

 history within the hen's body is the same and an apparently 

 normal egg is laid. If the hen has not been previously mated 

 and there are no spermatozoa in the oviduct to unite with 

 the ovum, the egg is called infertile and will not start to 

 develop when placed at incubating temperature. Such an 

 egg is the equal of a fertile egg for food purposes, and very 

 much superior for preserving, shipping, or storage purposes. 



Freak Eggs. — ^There are various kinds of abnormal eggs 

 that appear in flocks of any size with more or less frequency. 

 The most common is the double-yolked egg, which is caused 

 in two ways: two yolks may develop in one follicle, be 



' Pearl and Curtis, Journal Experimental Zoology, vol. xii, No. 1. 

 « Maine Bulletin No. 228. 



