Spermatocytes, spermatids, and spermatozoa from the testes of the two Peracaridae Praunus inermis Rathke (Myscidacea) and Iphinoe trispinosa (Cumacea), were examined in this study. In secondary spermatocytes extranuclear, electron-opaque masses were observed juxtaposed to the nuclear envelope only at nuclear pore regions. The nuclear envelope elsewhere lacked pores. Peripherally associated mitochondria surrounded these electron-opaque bodies. The bodies are morphologically identical to chromatoid bodies described in male germ cells of other animals. In early spermatids the mitochondrial-surrounded, chromatoid bodies were frequently seen in close proximity to Golgi complexes. Chromatoid bodies appear as a granulofibrillar, mottled network. Chromatoid bodies seen in later spermatids lacked peripherally associated mitochondria, although they maintained their close proximity to the Golgi complex. Suggestive evidence demonstrated Golgi membrane vesicle dissolution and a mixing of Golgi vesicle contents with the material composing the chromatoid body. In later spermatids the chromatoid body is found between the nucleus and the acroblast. During final spermatid maturation the material of the chromatoid body undergoes condensation which ultimately results in the formation of a rod-like structure similar in its position to subacrosomal substances such as perforatoria described in other spermatozoa. The significance of the origin of the subacrosomal rod-like structure from the chromatoid body and its possible function in oocyte activation following fertilization are discussed.