Electron Microscope Studies on Structure of Mitotic Figure. ∗

Summary

The metaphase spindle of the maturation division in the crayfish testis seems to be composed largely of longitudinally oriented “chromosomal fibers” measuring about 1500–2500 Å in width. These fibers appear to be compound, i.e., made up of smaller fibers of about 300–600 Å in width. Both the “chromosomal fibers” and their smaller fibrous components may at times show banding, which is possibly the result of irregular contraction during fixation. The centrioles appear relatively dense, are irregular in outline, and are probably not homogeneous bodies. The “chromosomal fibers” and astral rays lose their usual orientation at the periphery of the centriole. “Interzonal fibers” are relatively small in the late anaphase stages of the crayfish testis. Though “continuous fibers” were not clearly observed, we do not wish to claim that such fibers may not exist. Astral rays are composed of fibers, oriented as described in the past. The coagulated cytoplasm presents the appearance of a sponge-like reticulum, which is probably mostly a protein “framework,” since much of the other materials had been removed by the method of preparation.