Variation in the Development of Embryos of Hens’ Eggs

THE embryonic chick at the time of the laying of the eggs is usually subjected to the most extreme variations in environment it will have to withstand before hatching. In cold weather it may be quickly chilled, and during hot weather it may continue to develop, without pausing, for several hours before being stored under conditions that stop development while being held before incubation. Patterson (1910) found that the embryos show variation in development at the time of laying and Hutt and Pilkey (1930) have pointed out that some embryonic stages may be especially sensitive to external conditions, which may cause abnormal development or death, but would not affect the embryo at other stages. Hays and Nicolaides (1934) considered the variation, in embryonic development of fresh-laid eggs, among hens to be of primary importance, and stated that high hatching hens laid fertile eggs with more fully developed embryos than low . . .