NUCLEAR CHANGES DURING SPERMIOGENESIS IN A PULMONATE SNAIL

Abstract

Sperm head development in Otala lactea was studied with the electron microscope. The early spermatid nucleus is spherical and contains nucleoii and small filaments and granules organized into a sponge-like mass. Soon, the head flattens in a direction perpendicular to the future sperm axis and the contents of the nucleus begin to orient themselves into thin plates more or less parallel to the spermatid axis. Next, the head begins to elongate parallel to the spermatid axis and the intranuclear plates grow larger but still keep their orientation parallel to this axis. The plates may be several microns in length, of varying width (up to 1[mu]), about 60 A thick and spaced about 100 A apart. Toward the end of spermiogenesis the nucleus loses axial symmetry and begins to twist to form the mature, flame shaped head. At this time, material appears to be deposited between the plates so that in the mature sperm head (and in the advanced spermatid head) the plates are no longer visible.