Developmental features and synthetic patterns of male germ cells ofUrechis caupo.

The process of spermatogenesis in the echiuroid marine wormUrechis caupo takes place in the coelomic cavity. The nuclei of primary spermatocytes become gradually condensed from the G1 to G2 stages. The autoradiographic results show that the rate of RNA synthesis in these cells decreases considerably; no appreciable RNA synthesis is detected in cells in the G2 stage, meiosis, and in various stages of spermiogenesis. Synthesis of proteins, such as histones, protamines and also acrosomal basic protein, occurs during spermatogenesis when little or no RNA is made.