Natural History of the Ornate Box Turtle, Terrapene ornata ornata Agassiz

by John M. Legler

Increase in size following emergence from hibernation may be due in part to proliferation of the sustentacular cytoplasm. Decrease in size in early June is correlated with the end of the period of most active mating; maximal size is coincident with the peak of the spermatogenic cycle in early September.

Fig. 3. Seasonal fluctuations in size (average greatest diameter) of testes in T. o. ornata as determined by examination of 40 specimens from eastern Kansas.

Spermatogenesis (refer to [Pl. 19, Figs. 1-5]) begins in early May when a few spermatogonia appear in the seminiferous tubules. The histological appearance of testes preserved in April and May is much the same. Nuclei of Sertoli cells, which outnumber the spermatogonia, are evident at the periphery of the tubules and the clear cytoplasm of the cells extends into and nearly fills the lumina. The few darkly stained spermatids that are present in April are cells that probably were produced in the previous summer. Sperm are present in small groups within the sustentacular cytoplasm, but ordinarily are absent in the lumina.

Primary spermatocytes appear in the tubules from mid-May to early June. By mid-May there are practically no sperm at any place in the tubules. The sustentacular cytoplasm has a less compact arrangement in late May than in April.

Spermatogenesis is well under way by mid-June; at this time, two or three distinct layers of primary and secondary spermatocytes are present and these cells outnumber the Sertoli cells. The lumina are filled with cellular detritus and are no longer bordered by a clear ring of sustentacular cytoplasm. No sperm are present.

Spermatids appear in late June and a few of them undergo metamorphosis in early July; by mid-July, spermatids and secondary spermatocytes are the dominant cells in the seminiferous tubules, although spermatogonia are still active.

By late August, clusters of sperm and metamorphosing spermatids surround the Sertoli cells; large numbers of sperm as well as sloughed cells representing various spermatogenic stages are present in the lumina. Secondary spermatocytes are still evident near the periphery of the tubules but they are much less numerous than spermatids. The germinal epithelium is still semiactive and small groups of primary spermatocytes are present in nearly all of the tubules.

The spermatogenic cycle is completed in the latter half of October when most of the spermatozoa pass into the epididymides. A few spermatozoa and spermatids remain in the seminiferous tubules during hibernation. Although no testicular material was obtained from hibernating turtles, comparisons of sections made in October and April show that the germinal epithelium remains inactive from autumn until spring. Possibly some spermiogenesis takes place in the early phases of hibernation or in the period in late autumn when turtles are intermittently active. It is uncertain whether the reorganization of the sustentacular cytoplasm occurs in autumn, in spring, or in the course of hibernation.