I t is a common observation that in the domestic fowl egg laying is normally restricted to the daylight period. The few eggs produced at night are usually without shell o r with a poorly formed one, indicating that they were prematurely expelled. Atwood ( '29) has shown that since somewhat more than 24 hours usually expires between layings, each successive egg of the clutch is laid a little later in the day. Usually, when the clutch position is such that the egg is laid after the middle of the afternoon, the next egg is not laid at the usual interval, but a day is missed and a new series is started with a morning egg. Thus, most eggs are laid between 7 A.M. and 5 P.M. Since the egg normally requires about 24 to 28 hours for formation (Warren and Scott, '35) the question arises as to what is the regulatory factor preventing the laying of eggs a t night. Is there a general retardation of the egg formation processes during the night, or is the failure to lay a t night brought about by some other means?
Considerable work (Bissonnette, '33) has been done relative to the influence of light on the onset of sexual maturity (spermatogenesis and to some extent ovulation) in wild birds. However, the problem here is of a different nature, since phenomena controlling the rate rather than the onset of egg production are under consideration.
Contribution no. 94, Department of Poultry Husbandry.