In the seminiferous tubules and interstitium of the viper there occur cyclical changes basically similar to those in birds and the pike. These involve the metamorphosis of unshed germinal material into cholesterol-positive Iipids, the rehabilitation of the interstitium after the seasonal depletion of its cytoplasmic Iipids and cholesterol shortly after the spring emergence from hibernation, and the completion of spermatogenesis after basking in the sun. The viper differs from birds in that its tubule Iipids contain much less cholesterol; also, the subsequent spermatogenesis begins almost immediately (as in poikilothermous pike and frog), and proceeds to the spermatid stage in the presence of such Iipids. Further, although in some individuals new Leydig cells rapidly mature, this resurgence is delayed in others. Thus, although the succeeding spermatogenesis always begins in still-lipoidal tubules, it may do so in the presence of a largely non-lipoidal interstitium. Mitoses were observed in mature Leydig cells. Fibroblasts occasionally alter to take on an apparently glandular function.
By July most animals had regained a heavy lipoidal and cholesterol-positive interstitium, lost most of their tubule Iipids, and possessed either secondary spermatocytes or, sometimes, spermatids. This internal activity is probably partly responsible for autumnal sexual behaviour. Factors additional to temperature control spermatogenesis, for only a few spermatozoa are formed by the time of hibernation in October. No pronounced retrogressive changes occur during hibernation: the cycle merely halts, and begins without further delay on emergence. Thus spermatogenesis may be at its peak by the end of March.
The expanded, glandular ‘sexual segment’ of the male renal tubule also exhibits cyclical changes involving the production and expenditure of cholesterol-positive Iipids, but such changes take place also in narrow parts of the tubule and, further, in the kidney of the female.