Electron microscope study of spermiogenesis inCaiman crocodylusL.

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Abstract
Spermiogenesis in Caiman crocodylus was examined by electron microscopy. The acrosomal complex, the perforatorium and the growing axoneme of young spermatids are described. During the nuclear elongation of intermediate spermatids, two ≪manchettes≫ of microtubules were observed in addition to the acrosomal complex, perforatorium growth and chromatin condensation. At the onset of spermatid elongation, there is a set of microtubules around the nucleus and, at the end of elongation, a second set of microtubules parallel to the main axis of the cell appears. Both circular and longitudinal manchettes were observed together. In the neck‐region a striated structure of electron‐dense material is found on one side of the distal centriole. The descent of the mitochondria into che middle‐piece of the tail occurs only in the last stage of differentiation. The mitochondria are small, their cristae are irregularly arranged and the centres of the mitochondria consist of an electrondense material. Unlike most other reptilian sperm, the ring‐shaped sheath is not present in the middle‐piece. From the comparative data we conclude that the sperm of this alligator is more similar to the turtle spermatozoa than to spermatozoa of other reptiles.