Morphological changes in eupyrene and apyrene spermatozoa in the reproductive tract of the male butterfly Atrophaneura alcinous Klug

Eupyrene and apyrene spermatozoa are contained in separate cysts in the tes tis of the butterfly Atrophaneura alcinous. Spermatozoa of both types from various parts of the male reproductive tract were examined with particular reference to their morphological characteristics. All spermatozoa collected from the vas deferens and the vesicula seminalis were found to be immotile under a dissecting microscope. No spermatozoa of either type were recogniz ed in any part of the ejaculatory duct. Within the testis, eupyrene spermat ozoa are present in bundles and each spermatozoon has a slender nucleus wit h an acrosome and a long flagellum containing mitochondrial derivatives. Tw o kinds of appendages, lacinate and reticular, are present on the surface o f the sperm membrane. They are replaced with an extracellular sheath during passage through the vas deferens. In contrast, apyrene spermatozoa have ne ither nucleus nor acrosome, whereas a cup-shaped structure was found at the sperm tip instead of the acrosome. Unlike eupyrene spermatozoa, they are s urrounded by a concentric sheath outside the sperm membrane in the vas defe rens. Individual apyrene spermatozoa and coiled bundles of eupyrene spermat ozoa were both found to accumulate in the vesicula seminalis before mating. These morphological changes during passage through the male reproductive t ract suggests the occurrence of a kind of maturation and capacitation proce ss reminiscent of mammalian spermatozoa.