Morphology of the ovary of Caiman crocodilus (Crocodylia: Alligatoridae).

We describe the ovarian histology and characterize the folliculogenesis of adult females of Caiman crocodilus in order to compare them with other species of Reptilia. The gonad has a thin irregular cortex and a well-developed reticular stroma, composed of vascularized chordae, drained by large lymphatic vessels and separated by extensive lacunae. Simple cuboidal to squamous epithelium, dense connective tissue with numerous elastin fibers, and smooth muscle constitute the ovarian wall. This morphology is similar to that of other Crocodylia, Aves and Testudines. Germinal nests are distributed in the ovarian cortex, some of them with oogonia. Oocytes leave the germinal nests with a single layered cuboidal granulosa, remaining simple during vitellogenesis, as in other Archosauria and Testudines and different from Squamata. As the oocyte grows, the theca is formed by numerous fibroblasts, collagen fibers, and smooth muscle fibers, becoming very thick, highly vascularized and developing muscle bands at advanced vitellogenesis. Folliculogenesis shares morphological features with other species of Reptilia. The corpus luteum is similar to that described for Archosauria; during luteolysis, the theca shrinks and the amount of luteinic cells decreases. The relationship of the corpus luteum to vitellogenesis and egg maintenance is unclear in Crocodylia. Follicular regression in Caiman crocodilus corresponds to an invasive atresia type. Histological features seen in the ovary of Caiman crocodilus are similar to those described in Alligator mississippiensis indicating that these features could be shared among Crocodylia. Also several of these morphological characteristics are observed in Aves suggesting a similar reproductive functional morphology in Archosauria.