1. A report that total darkness is more effective than illumination in the production of spermatogenesis in young of the xerophilous budgerygah is shown to be due to a misinterpretation of results.
2. An internal rhythm of reproduction allows young male zebra finches (like young budgerygahs) to produce spermatozoa within 60 days in almost total darkness when provided with plenty of food and water at laboratory temperatures. Oocytes enlarge only slightly. Both sexes come into breeding dress in the dark.
3. Various conditions of illumination (including decreasing photoperiods) cause in both sexes greater gametogenetic activity than occurs in darkness.
4. Both budgerygah and zebra finch are xerophilous. They are opportunist breeders after rainfall, irrespective of season. Although they retain an ancestral capacity to respond to photostimulation, any such tendency under natural conditions could be over-ridden by external inhibitors.
5. The rapid production of spermatozoa (within 60 days) is in both parrot and finch a physiological aspect of drought adaptation enabling very young birds to reproduce quickly whenever environmental conditions are propitious.