ONTOGENY AND ULTRASTRUCTURE OF SEMINAL-VESICLES OF THE CATFISH, CLARIAS-GARIEPINUS

The ontogenesis and structural characteristics of the seminal vesicles in Clarias gariepinus (sharptooth catfish) were studied by light and electron microscopy and are described in detail. The seminal vesicles, beginning as simple protrusions from the vas efferentia, becomes more complex with age. Their distal ends become fingerlike and the bases f orm palm-like extensions. Juvenile male organs do not reveal any signs of seminal vesicles although spermatogenic tissue is already well del ineated. The developing gonads contain clusters of large cells, close to the sperm duct and cysts of the testis, from which seminal vesicles are formed. Secretory epithelium lines the tubules of the seminal ves icles and becomes columnar as the tissue matures. Electron micrographs of these epithelial cells reveal two types of cells: opaque cells and cells with very vacuolized cytoplasm. Dense pinocytotic vesicles are present between the membranes of neighbouring seminal tubules and apic al cell membranes facing the lumen. Maturation and onset of secretion by the secretory cells is accompanied by morphological changes. Protru ding cylindrical cells become shortened, modified to cuboidal, rounded cells that send tubular extensions into the lumen. In the final stage of differentiation, only connective tissue membranes supporting the t ubule walls remain intact. At the points of contact between the testis , seminal vesicles, and sperm duct, the epithelia of these organs ofte n become confluent. The distal parts of the seminal vesicles, rarely c ontain sperm; during spawning sperm accumulated in the proximal tubule s of the vesicles, (C) 1994 Wiley-Liss, Inc.