Spermiogenesis in the gall-midge Monarthropalpus buxi (Cecidomyiidae, Diptera)

In Monarthropalpus spermiogenesis only two spermatids, orthogonally oriented, and a large residual cell are formed from each spermatocyte. The three cells are mutually connected through a cytoplasmic bridge. Later, the residual cell degenerates, Golgi systems are present in early spermatids; they never originate acrosomal vesicles and are eliminated with remnants of cytoplasm at the end of cell maturation. Mitochondria, always isolated, are localized in the postnuclear region in the early stage but, during spermiogenesis, they migrate anteriorly, in front of the nucleus. Microtubules are present during the whole spermiogenesis but they disappear at cell maturity. The aberrant axoneme of the motile spermatozoa is formed by a large number of microtubular doublets, each having only an outer dynein arm.