Modification of mammalian sexual cycles, VII—Fertile matings of raccoons in December instead of February induced by increasing daily periods of light

Since Bissonnette (1932, 1933,1935 a, b) discovered that the sexual cycles of ferrets could be altered at will by modifying the seasonal light cycles to which they were exposed, and Baker and Ranson (1932a, b, 1933) found that field mice were susceptible to similar changes by manipulation of both food and light cycles, many other studies of sexual photoperiodicity in mammals have been made. These have shown that different species show differences from each other in this respect. Bissonnette has reviewed the literature on sexual photoperiodicity in both animals and plants (Bissonnette 1935 c, 1936a, b), and his papers may be referred to for a more complete treatment of the subject. Some animals, like guinea-pigs and 13-lined ground squirrels, are almost if not quite unaffected by changes in duration of exposure to light, at least within very broad limits. Some, like ferrets, come into sexual activity on increasing daily exposures to light. Others, like sheep and deer, become sexually active on decreasing days. And still others, like hedgehogs and field mice, are caused to change their breeding or sexual cycles by other environmental factors as well as by changes in length of day. An attempt has been made to test the relation of raccoons, Procyon lotor (Linn.), to such alterations of daily duration of light. These experiments were carried out at Shade Swamp Sanctuary, Farmington, Connecticut, where the junior author is resident director. Mr Earl E. Bailey of Trinity College, Hartford, Connecticut, took care of the electrical arrangements.