THE SO-CALLED CENTRAL BODIES IN FERTILIZED ECHINARACHNIUS EGGS

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Abstract
When metaphase asters of the 1st cleavage of Echinarachnius eggs were fixed in a wide variety of reagents, centrosomes (the large diffuse type of central body) were found only in those cases where rays were distinctly coagulated to the astral mid-region. When rays were not fixed, centrosomes were absent, even in those cases where spindle fibers were distinct. This indicates that the supposed centrosome is a coagulation product of the focal area of well formed rays. There are no centrioles; occasionally they are simulated by cytoplasmic granules which by chance occur near the astral center. It is probable that central body phenomena in Echinarachnius are typical for echinoderms. Illustrations in previous studies of echinoderm central bodies show three classes: (1) a minute centriole surrounded by a larger centrosome, (2) a centriole only, (3) a centrosome only. It is suggested that previously described echinoderm centrosomes are the coagulated focal region of astral rays misinterpreted and that the centrioles are misinterpretations of cytoplasmic granules. These results may possibly have application to animal cells in general (not including spermatocytes); they necessitate re-examination of current central body hypothesis, since central bodies in echinoderms have been regarded as "typical." The differences between previous conclusions and those of the present investigation are probably explained by differences in methods.

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