A light and electron microscopical study of spermatogenesis in <i>Hydra cauliculata</i>

Abstract

Morphological changes in the interstitial cells were studied during their differentiation into spermatozoa. Development of the spermatogonium involves an increase in nuclear and nucleolar size, and the formation of a dense mass of cytoplasmic ribosomes. The mature spermatozoon has a relatively simple structure. The head consists of a bullet shaped, homogeneous nucleus, which lacks an acrosome but bears distal membrane specializations. The middle piece is composed of four large spherical mitochondria at the base of nucleus. A single flagellum projects from one of the two centrioles lodged between the mitochondria. The flagellum appears early during development in the primary spermatocyte. During spermiogenesis microtubules associated with the basal body flagellum complex appear to define the axis of chromatin condensation.