ELECTRON MICROSCOPE STUDIES ON SPERM DIFFERENTIATION IN MARINE ANNELID WORMS. II. SPERM FORMATION IN ARENICOLA BRASILIENSIS

The course of spermiogenesis in arenicola brasiliensis was observed with the electron microscope. The spermatogonia floating in the body cavity seem to proliferate and differentiate to mature spermatozoa in the coelomic fluid. More than a hundred spermatids are connected to one large central mass of cytoplasm and spermiogenesis proceeds synchronously in one cluster, which changes into a sperm-disc during maturation. The pre-acrosomal vesicle originates from the Golgi-body and gradually changes into the acrosomal vesicle of peculiar structure like a cup upside down. In the process of differentiation of the acrosome, a part of the material in the acrosomal vesicle is transferred into the space between the vesicle and the nucleus. The posterior one-third of the cylindrical nucleus is surrounded by four middle-piece mitochondria. The flagellar axoneme originates from one of the centrioles, which is located near a posterior pit in the nucleus.