Novel organization of the spermatozoon in two species of murid rodents from southern Asia.

The morphology and structural organization of unusual spermatozoa from two species of bandicoot rats (Bandicota spp) from Southern Asia were studied with the light and transmission electron microscope. Unlike those described for nearly all other eutherian species the heads of Bandicota savilei and B. indica spermatozoa were bulbous or globular in shape and had no narrow uniformly defined apex nor a clearly delineated perforatorium. The nucleus, which had one or more prominent vacuoles, was capped by a huge, bulky, acrosome with no obvious morphologically recognizable equatorial segment. The postacrosomal dense lamina was extremely short and a posterior ring lay anterior to the caudal pole of the nucleus. In addition, the tail of the spermatozoon was only 28-45 microns in length. The organization of the spermatozoon of these two species of Bandicota is thus quite unlike that described for any other murid rodent or even mammalian species. Its highly divergent features suggest that the processes of zona penetration and incorporation of the fertilizing spermatozoon into the egg may differ markedly from those of all eutherians so far investigated.