SEASONAL CHANGES IN THE DISTRIBUTION OF THE TESTIS LIPIDS OF THE CASPIAN TERRAPIN CLEMMYS CASPICA

The testis of Clemmys caspica undergoes a sequence of well defined cyclical events. These include a seasonal enlargement of the Sertoli cells and the genesis of large quantities of lipoidal material in their cytoplasm. Intra‐tubular lipids disappear at the onset of the following spermatogenetic rhythm. This seasonal accumulation of dense sudanophil material within the seminiferous tubules and its disappearance prior to spermatogenesis is comparable with the events which occur in seasonal birds and other sub‐mammalian vertebrates. A lipid cycle occurs also in the interstitial Leydig cells which become denuded of their lipid contents at a time when spermatozoa are being discharged from the epididymal canals. This is the time of maximum sexual activity. By September the seminiferous tubules have reached a peak of spermatogenesis and contain bunched spermatozoa. This is then followed by the transference of spermatozoa from the tubule lumena into the epididymal canals where they are stored for several months until the following breeding season. Meantime the ‘spent’ tubules become collapsed and enter a period of sexual negativity. In this, the terrapin differs from the viper ( vipera berus ) where the next spermatogenetic rhythm begins almost, immediately after the spring shedding of spermatozoa and becomes well‐established whilst the tubules are still clotted with large quantities of post‐nuptial lipids. The spermatogenetic cycle closely parallels the environmental temperature cycle. It commences in April when environmental temperatures are rising rapidly and does not start to decline until October, by which time the daily temperature is beginning to drop. This cycle commences whilst day‐lengths are increasing, but declining day‐lengths after the summer solstice (21st June) appears to have no effect on spermatogenesis which continues unabated until late September.