Abstract
1) The central body of the silkworm was traced in unbroken continuity from resting spermatogonia to spermatids, and the observations were compared with those in other animals.
2) Each spermatogonium exhibits a centrosome, which consists of an idiozome and a pair of short rod-shaped centrioles at the midst of the idiozome.
3) At the beginning of the growth period of the primary spermatocyte, each centriole divides into a pair of globules, so that two pairs of spherical granules are produced in each cell. At the second contraction stage, the centrioles move out of the idiozome into the area between the cell surface and the idiozome. The four centrioles elongate into elliptical or rod-shaped bodies, each extruding an axial filament from the distal tip and they are frequently in contact two by two at the proximal tips, forming two V's. The idiozome disappears in the dispersion stage.
By the diakinesis stage, the centrioles divide again into four pairs of spherical granules. Thus, two pairs of spherical centrioles are distributed to each pole of the first maturation division.
4) During the telophase and interkinesis, the two pairs of centrioles separate and move until they reach the positions 180° apart, so that a diplosome is found at each pole of the second maturation division which is distributed unchanged to each spermatid.
5) It is most significant that the centrioles increase in number up to the diakinesis stage to become as many as in all four spermatids together, and so the total amount of centrioles remains unchanged throughout the two meiotic divisions, in marked contrast with the somatic divisions. This relation is in agreement with the majority of extensive observations carried out by many authors on various animal species.
