No abstract

Spermatozoa in the head of the epididymis of the flying squirrel have large cup-shaped acrosomal heads with two ventral ridges. The cytoplasmic droplet contains an ovoid body and a group of large granules. These structures may be related to the chromatoid body of spermatids. The spermatozoa form polarized cylindrical bodies with centrally placed tails and peripheral heads. The tips of acrosomes protrude into concavities of acrosomal cups of neighboring spermatozoa. Peripheral portions of acrosomes are in contact with microvilli (stereocilia) of epididymal cells. Polarized cylindrical bodies are present in five species of Sciuridae.Light microscopic examination of the caput epididymis of the flying squirrel (Glaucomys volans) reveals that the spermatozoa are regularly arranged to form polarized cylindrical bodies (Martan and Hruban, '70). The heads of spermatozoa are located at the periphery of the polarized cylinders and the tails are in the center of these bodies. Similar arrangement of epididymal spermatozoa is observed in other members of the family Sciuridae, such as the grey and fox squirrels (Martan, Adams and Perkins, '70), chipmunk and 13-lined ground squirrel (Unpublished observations).The present study is concerned with the fine structure of certain aspects of spermatozoa and their spatial relationship in the caput epididymis of the flying squirrel.Two adult male flying squirrels (Glaucomys volans) were killed in early March.They were trapped as young animals in Southern Illinois and kept outside in a large cage for one and half years. Three females introduced into the cage during this time became pregnant. Samples of the head of epididymis were fixed at 5°C in paraformaldehyde (Lynn, Martin and Race, '66), postfmed in 1% osmium tetroxide, buffered with s-collidine buffer (Bennett and Luft, '59) at pH 7.4 and embedded in Epon (Luft, '61). Thin sections were cut MATERIALS AND METHODS J. MORPH., 135: 87-98with a Porter-Blum microtome, stained with uranyl acetate and lead citrate. Selected areas were photographed in Siemens Elmiskop IA. Light microscopic studies were reported previously (Martan and Hruban, '70). RESULTSThe fine structure of the spermatozoa in the caput epididymis of the flying squirrel is in principle the same as that of other mammalian spermatozoa (Fawcett, '58, '65, '70; Fawcett and Ito, '65; Nicander and Bane, '62). The terminology used in articles by Fawcett is used here. The spermatozoa differ mainly in the shape of their heads and in the structure of the cytoplasmic droplet. Our description is limited to these structures.The nucleus is flattened dorsoventrally and is concave on its dorsal surface ( figs. 1, 3, 13). The acrosome is very large. Sagittal sections reveal a complex shape ( fig. 3) of the acrosomal cap resembling that of the ground squirrel (Fawcett, '70). While the acrosomal cap of the guinea pig sperm has one prominent horse-shoe shaped elevation on its upper surface (Fawcett, '65, ' 7 0 ) , the acrosomal cap of the flying squirrel has two horse-shoe shaped ele-