1. In the heads of maturing sperm of a locust the chromatin becomes arranged in a highly regular manner so as to produce many parallel lines about 60 A thick in longitudinal section and contiguous polygons in transverse section.
2. This configuration appears after fixation in osmium tetroxide, formaldehyde, or acetic acid; intermediate stages in its development are illustrated.
3. These electron micrographs are interpreted to mean that, during sperm maturation, the chromatin becomes formed into sheets and then into tubes running parallel with the long axis.
4. In the mature sperm head we have been unable so far to detect this structure. This may be because the chromatin becomes so compact during the shrinkage of the nucleus which occurs during formation of the mature sperm.