Spermatogenesis and sperm dimorphism in land slug Arion after L. (Pulmonata, Mollusca)

The fine structure of spermatogonia, spermatocytes, spermatids and spermatozoa has been examined in the hermaphrodite gland of Arion ater in detail. Intercellular bridges link spermatogonia, primary and secondary spermatocytes and spermatids. The primary spermatocytes appear in groups, connected to a common cytoplasmic mass, the Cytophore. Two types of spermatids and sperm are recognized (eupyrene and apyrene). The apyrene spermatids differ from the eupyrene type, particularly in the later spermatid stage, by residual cytoplasm with many vesiculose bodies around the nucleus, which is electron-dense. The eupyrene sperm have an acrosome and DNA-histone fibers in the nucleus. Organelle function of the spermatogenic cells at different stages of differentiation, and also the occurrence of sperm dimorphism have been discussed.