Spermiogenesis and spermiation in the Japanese quail (Coturnix coturnix japonica).

The ultrastructure of 12 steps of spermatid development and the process of spermiation are described for the Japanese quail in order to clarify the classification proposed for determining the stages of the cycle of the seminiferous epithelium (Lin et al. 1990) and to assess disagreements in the literature about sperm development in birds. It was concluded that acrosomal development involves the formation of proacrosomal granules which do not contain dense granules like the mammalian acrosome. Material which forms the perforatorium initially accumulates as a nuclear granule before appearing in the subacrosomal space. A circular and longitudinal manchette develop sequentially during nuclear elongation. Microtubules of the circular manchette initially form around several parts of the spherical nucleus of step 4 spermatids and subsequently occur most frequently around the narrowest regions of the elongating nucleus. Fibrous sheath development starts in step 2 spermatids indicating that it forms much earlier in the quail than in mammals. Spermiation differs from the process described in mammals in that the residual body is released from near the rostral end of the sperm nucleus leaving no cytoplasmic droplet in quail spermatozoa.