Seasonal changes in testicular histology of three species of the lizard genus Uma

Desert‐dwelling male Uma notata, U. inornata and U. scoparia were autopsied monthly from 1959 through 1962. Seasonal changes in the histological morphology of the testes were observed. A series of eight stages, indicating these changes in spermatogenic activity, was established. These categories arbitrarily divide a continuous process into several recognizable stages. Present evidence indicates that male breeding cycles can be determined rather precisely by examining any of several reproductive features. Data from several sources reveal that the male breeding season of U. scoparia is shorter than that of U. notata or U. inornata . Nevertheless, the testes of all three species appear to function reproductively during the hottest month of the year. Possible explanations for this ability are suggested. Little difference was observed in the time the seminiferous tubules of U. notata testes reached full breeding condition (stage 6) following dry winters. This is in contrast to the time motile sperm appeared at the cloacal end of the vas deferens in these animals. Thus is appears that the major cause of postponement in male U. notata reproductive activity following dry winters is due to a delay in sperm reaching the vas deferens rather than a retardation in sperm production.