Ultrastructural investigation of the corpora atretica of the electric ray, Torpedo marmorata.

Follicular atresia was studied in the ovary of the electric ray, Torpedo marmorata, by light and electron microscopy. The course of atresia may be divided into four stages. The first two comprise the dissolution of the oocyte and its phagocytosis by the small cells of the granulosa epithelium. The third stage consists of the transformation of the granulosa epithelium into an active glandular structure and is accompanied by the development of a smooth endoplasmic reticulum. The fourth stage is marked by sclerosis and pigmentary degeneration of the atretic follicle. Together these observations suggest an endocrine steroidogenic role for the corpora atretica (preovulatory corpora lutea) in T. marmorata.