Ovarian folliculogenesis in the oviparous Mexican lizard Ctenosaura pectinata

The ovarian follicles of Ctenosaura pectinata exhibit a clear seasonal cycle in morphology. Early in development, each oocyte is surrounded by a granulosa composed of a single layer of cuboidal or squamous cells and thin thecal layers. As folliculogenesis progresses, the granulosa becomes multilay- ered and composed of three distinct cell types. After vitellogenesis begins and active sequestration of yolk into the ooplasm is initiated, the granulosa is reduced to a single cell type. We observed a striking change in the appearance of the ooplasm during folliculogenesis. Early ovarian development is character- ized by an ooplasm with homogeneously distributed fine fibrils, but as develop- ment progresses, the ooplasm contains dense clumps of fibers aggregated into distinctive bundles. The ooplasm displays further complexity in morphology as previtellogenic growth continues and as different regions exhibit various combi- nations of fibers and vacuoles. Yolk platelet formation is complex, with distinc- tive stages generating platelets with varying morphologies. 6: 1996 WiIey-Liss, Inc. Ovarian follicular development is an essen- tial reproductive phenomenon in all females. In reptiles, ovarian follicular growth involves not only the growth and maturation of the oocyte, but also requires the storage of large quantities of yolk in the ooplasm (see Gu- raya, '89). Although the general sequence of folliculogenesis has been described in a num- ber of reptiles, some variation among species has been reported (e.g., Loyez, '06; Boyd, '40; Miller, '48; Wilhoft, '63; Goldberg, '70; Hubert, '71a,b; '73, '74, '76, '77; Guraya, '78; Varma, '70; Laughran et al., '81; Klosterman, '83, '87; van Wyk, '84; Uribe et al., '95). In particular, there is still a need for informa- tion on the cytoplasmic changes occurring during oocyte growth and vitellogenesis in most reptiles. As in all vertebrates, the reptilian ovarian follicle is composed of a central oocyte, sur- rounded by a bilayered, acellular membrane, the zona pellucida. As follicular development progresses, the zona pellucida is clearly sub- divided into two distinct regions, an outer homogeneous layer adjacent to the granulosa and an inner, thicker striated layer (zona radiata) lying against the oolemma (Varma, '70; Jones et al., '75; Guraya and Varma, '76;