The Effect of Light on Maturation and the Estrous Cycle of the Cotton Rat, Sigmodon Hispidus Hispidus1

IN RECENT years a large number of investigations have shown that reproductive activity in some cold-blooded vertebrates, in many birds and in various mammals is modified by the length of day. A number of reviews of the subject are available (Bissonnette, 1936a; Bissonnette, 1937; Marshall, 1936; Rowan, 1938a; and Rowan, 1938b). Since the research to be presented here deals with a mamma−lian form, a short review of previous work on mammals is included. Some mammals, such as the guinea pig (Dempsey, Myers, Young and Jennison, 1934), the rabbit (Smelser, Walton and Whetham, 1934), the hedgehog (Allanson and Deanesly, 1934) and the ground squirrel (Wells, 1935), are apparently not influenced to any marked extent by experimental variation of day length and light intensity. Increased day length in the fall produced estrus in winter in the ferret (Bissonnette, 1932) and caused breeding to be advanced 6 weeks in the raccoon (Bissonnette and Csech, 1937).