Bissonnette ('30 et. seq.) first showed for the male starling that periods of artificial illumination, usually of about 6 hours when added daily to natural fall and winter day-lengths, will induce a precocious spermatogenesis. In an opposite direction, a reduction in the daily length of exposure to light to 10 hours will cause testes already in spermatogenesis to involute. Tn a long series of studies during the early thirties, Hissoririette expanded on these primary observations by show- ing that the spci-matogenesis induced by pliotoperiotlic manipulations was influenced by the wave-length and the intensity of the added illumination. In addition, a large anloinit of other clarifying and supplementary riiatcrial was reported (compare Bissonnette, '37, f o r a general summary). The general conclusion made was "that it is the relative light ration as compared with previoiis rations and not [the] absolute light ration at any one time that determines the reaction of the germinal elements of the testis t o treatment" (Bissonnette, '31 a).
Continuing this work, a series of investigations (Burger ( '39 a, b) was begun with the purpose of learning the precise conditions whereby sexual activation is caused in the male l Aided by a grant from the American Philosophical Society, administered by