Abstract
Flagellar structure in spermatids of several species of cricket was studied with the electron microscope. The flagella of mid-spermatids contain the usual 9 + 2 set of fibers and a set of nine accessory fibers. At first all are hollow, then the lumina become filled with an electron-opaque matrix material in which narrow electron-lucent microcylinders are embedded. The accessory fibers and one central fiber become filled first, then the B subfibers and the other central fiber, and finally the A subfiber. In all but the B subfibers, microcylinders are arranged in a circular or oval group that lies against the wall of the lumen and encloses one or several additional microcylinders. In accessory fibers there are 9-11 microcylinders in the outer group and 4-5 in the inner group. In the central fibers and the A subfibers there are 7-9 microcylinders that enclose one or two more. In the B subfibers there is a crescentic group of 6-7 microcylinders that partially encloses 2-3 more. Microcylinders become packed as though they are independent units; the matrix appears to be an amorphous substance that fills the spaces around the microcylinders. The mean diameter of the microcylinders is 36 A, and they have a center-to-center distance of 56 A. In both respects they resemble wall subunits of flagellar fibers and microtubules and they may be similar structures but with a different localization. The diameter of accessory fibers is about 350 A, which is 25% greater than that of the other flagellar fibers and of cytoplasmic microtubules. Rotation tests suggest that the accessory fibers have 16 wall-subunits.