Diurnal Rhythm and Photoperiodism in Testicular Recrudescence of the House Finch.
A circadian rhythm in house finches appears to control the timing of the photoperiodic response of testicular recrudescence. A 6-hour light period coupled with dark periods of varying duration does not stimulate spermatogenesis in cycle lengths of 24, 48, and 72 hours, but initiates spermatogenesis in cycles of 12, 36, and 60 hours.
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