The structure and development of the seminiferous follicle in Scyliorhinus caniculus and Torpedo marmorata (Elasmobranchii)

Summary

A light microscopic and phase-contrast study of the developing seminiferous follicles in two elasmobranch species was made. After an initial period of independent mitotic divisions, each spermatogonium becomes entirely surrounded by a cytoplasmic extension of a single follicle cell (Sertoli cell). These bicellular units may be termed spermatocysts. This relationship remains through six succeeding germ cell generations, usually resulting in a group of 64 isogenous spermatids in each spermatocyst. Thus, all substances exchanged between the blood stream and the germ cells must pass through the body of the follicle cell. As the spermatids transform into spermatozoa, they are drawn into a compact bundle and are finally released from the follicle cell. Germ cell development is closely synchronous within each spermatocyst and spermatocyst development is synchronous within each follicle. Germ cell and Sertoli cell lines appear to be entirely separate. Intercellular cytoplasmic connections are retained among large groups of daughter germ cells. It is suggested that these cytoplasmic bridges as well as spermatocyst formation serve in promoting equality of physiological opportunity throughout the large germ-cell mass.