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Early spermatids of the crab, Pinnixia sp., are characterized by a large nuclear/cytoplasmic ratio. During early spermiogenesis an organelle, composed of pentalaminar membranes derived from the endoplasmic reticulum and nuclear membranes, is formed. Portions of this organelle become incorporated within a cylindershaped invagination of the acrosome. Portions of the nuclear membrane disappear beneath the acrosome resulting in intermingling of nucleoplasm, centrioles and mitochondria. The nuclear membrane elsewhere is found as a pentalaminar membrane underlying the plasma membrane. Centrioles are found in mature spermatozoa at the base of the cylinder-shaped acrosomal invagination, and mitochondria are found intermingled with nuclear remnants surrounding the acrosome. This datum is compared to previously described events in spermiogenesis of other decapod crustacea and arthropods exhibiting similar modes of spermiogenesis. It is concluded that the differences and/or similarities exhibited by centrioles and mitochondria in these forms could be significant in terms of subsequent zygote differentiation.Studies on the coalescence of cytoplasmic organelles and nucleoplasm have now been described in spermatozoa of several animals. These studies include the cray- genesis in different arthropods, Assuming that centrioles and/or mitochondria function in subsequent zygote development in these animals, the differences exhibited during spermiogenesis could have important genetic implications due to the absence or presence of these organelles (Granick and Gibor, '67; Nass, '69).The following study on spermatids and spermatozoa of the crab, Pinnixia sp., was made in order to extend such studies to another species of crustacea since datum on at least three of the above crustacea is conflicting. This either implies species differences in behavior of centrioles and mitochondria during spermiogenesis, errors in interpretation of data, or both. Studies on closely related and/or divergent crustacean types should help broaden our concepts about the possible genetic contributions of these organelles in such animals. MATERIALS AND METHODSFollowing ventral orientation of male Pinnixin S P .~ and incision into the ventral abdominal cavity, testes, vas dderens and seminal receptacle were removed and 1 Supported by U.S.P.H.S grant NB-06285.

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