Studies in Embryonic Mortality in the Fowl

Various studies upon the development of eggs of fowls and of pigeons have shown that the processes of formation of the egg and of development of the embryo during the passage of the egg down the oviduct are continuous throughout the twenty-four hours of the day. They are involuntary reactions. On the other hand the actual laying of the egg is a reflex for which the necessary sensory stimulus usually does not occur while the hen is on the roost at night. This means that if an egg be fully formed and ready to lay at 2 a. m., it is retained in the uterus till the following morning. The embryo of such an egg (when fertile) would presumably have undergone some six hours further development than if the egg had been fully formed at 2 p. m. and had been laid at 2:30 p. m. Such a view is . . .