V.—Summary.
1. The chromosomes of the second spermatocytes break up and the chromatin becomes diffused all through the nucleus. Later the chromatin collects in granules again and finally forms the walls of the tube-like spermatozoon head.
2. The spindle fibers break loose as the clear space is formed around the chromatin mass. They unite and contract, becoming fewer, thicker, and shorter. These bend and form the “striated nebenkern.” The fibers break up and sometimes show a blackberry appearance. Soon there is a collection of darker material at the center, surrounded by a clear space, which is shut off from the cytoplasm by a darkly staining membrane which in sections appears as a ring. This stage persists for some time; then the nebenkern moves against the axial filament, elongates, loses the ring, and the dark mass passes down along the axial filament. Often it appears in several small drops.
3. The axial filament does not come from the nebenkern nor from the acrosome. It comes apparently from the nucleus; probably from the centrosome closely attached to the nucleus. It never passes through the nebenkern—only over its surface.
4. The acrosome occupies a position in the angle between the nebenkern and the nucleus. It shows a central clear space surrounded by a darker mass which stains more intensely on one side. Later it passes to the front of the nucleus and forms the point of the spermatozoon head.
5. The mature spermatozoon consists of a sharp point, a slender, tube-like head filled with a clear fluid, and a long, thread-like tail.
Laboratory of Zoology and Histology,
University of Kansas.
September 27, 1901.