The differentiation and development of the testis in the lizard Calotes versicolor was studied histologically and histoenzymatically from the day of oviposition (stage 27) to 2 months after hatching. The study reveals the appearance of the gonadal component as a genital ridge at stage 27. The first sign of testis differentiation is observed at stage 33, which displays a well-developed medulla consisting of seminiferous cords comprising Pre-Sertoli cells. The sex differentiation of the embryonic gonads occurs at stage 34. At this stage, seminiferous cords of the testis are prominent and extensive with many pre-Sertoli cells and few spermatogonia. The interstitial space consists of immature fibroblast-type Leydig cells. Pre-Sertoli cells of the seminiferous cords differentiate into Sertoli cells with a triangular nucleus becoming apparent around stages 36-37. The fibroblast-like Leydig cells differentiate into round matured Leydig cells at stage 40. Quantitative estimation of germ cells reveals that the number of germ cells increases in individual gonads, and in 5-day-old hatchling's, this number multiplies by manifold. Spermatogonia show reductional division in the testis of 1-day-old hatchlings. Histochemical localization of Delta5-3beta-HSDH and G-6-PDH activity appears in the seminiferous cords (medulla) of the testis after sexual differentiation (stage 36), indicating that the embryonic medulla is the site of steroidogenesis and not the cortex in C. versicolor. This study also suggests that morphological differentiation of the gonad precedes detectable steroidogenesis in this species. In 10-day-old hatchling's, Delta5-3beta-HSDH activity is seen in the interstitial cells of the testis, which, however, is not detected in the seminiferous tubules. The intensity of the enzyme activity remains more or less the same in the testis up to 10 days after hatching and begins to increase thereafter. The increase in steroidogenesis parallels the progressive post-hatching increase of the interstitial/Leydig cells.

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The development of the ovary in the lizard Calotes versicolor has been studied histologically and histochemically from the day of oviposition (stage 27) to 2 months after hatching. The gonadal component appears as a genital ridge at stage 27. Sex differentiation of gonads occurs at stage 34, which indicates that the period of sexual bipotentiality is very brief. Oogenesis starts at stage 35, where preleptotene and leptotene oocytes appear for the first time in the ovary. The zygotene and pachytene oocytes appear during stage 36 and 38. Diplotene oocytes occur at stage 40. Folliculogenesis occurs 10 days after hatching. Follicles having a polymorphic membrana granulosa consisting of small, intermediate, and large round cells are found in 1-month-old hatchlings, and pyriform cells are observed in the granulosa of the ovary of 2-month-old hatchlings. The number of germ cells increases as development of the ovary proceeds. At oviposition, ∼236 and 244 germ cells were counted in right and left ovaries, respectively, and there was a manyfold increase in their number (to 4,234 and 4,294) at hatching. Mitotic germ cells are more abundant at stage 34, and no mitotic germ cells are seen after hatching. Histochemical localization of of  Δ5-3β-HSDH and G-6-PDH activity is seen in the medulla of the ovary after sexual differentiation (stage 36), which indicates that the medulla of the ovary is the site of steroidogenesis. intensity of the enzyme activity remains more or less the same in the ovary up to 1 month after hatching and begins to increase thereafter. © 1994 Wiley-Liss, Inc.

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