Abstract
The course of formation of the middle-piece of the mouse spermatozoon (Mus musculus) was studied in the fresh material by phase microscopy according to the liquid-paraffin method after Makino & Nakahara (1953). Further, the structure of the middle-piece of the mature spermatozoon was observed in the fixed material, and in the material treated with pepsin-HCl, or citric acid.
In living mature spermatozoa, the middle-piece shows no observable structure, being uniformly dense in appearance (Fig. 15). The early spermatid contains a fine centriole in close contact with the nucleus: a fine axial filament develops from the centriole. Along with the change in shape of the nucleus, the axial filament bends along the peripheral margin of the cell. The mitochondria migrate to the periphery of the cell, and arrange themselves along the long axis of the axial filament (Figs. 9-11). Then, the mitochondria form a string of beads after chain-like association, and coil around the axial filament in the form of spirals. After the completion of the sperm-head, the spermatozoon convertes into a well-elongated filamentous form, extruded from the cell body. At this time, it usually embraces a cytoplasmic mass (Figs. 6, 14). Meanwhile, the cytoplasmic mass seems to be absorbed by the middle-piece, and finally the mature spermatozoon is produced (Figs. 7, 15).
The observations of the smear preparations of spermatozoa fixed with Carnoy's fluid made it clear that the axial filament of the spermatozoon consisted of two fibers, each of which was made up of a certain number of fibrils (Figs. 17-19). After the treatments with pepsin-HCl, or with citric acid, it was demonstrated that a string of beads-like mitochondria coils around the axial filament (Figs. 24, 25).
