Effects of continual mechanical agitation prior to cleavage in echinoderm eggs

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Abstract
The force necessary to accomplish animal cell division is exerted by a ring of specialized cytoplasm which is rapidly established at the equatorial surface by the mitotic apparatus. Although the structure of the cleavage mechanism is not demonstrable before it is functional, the geometrical relation between the mitotic apparatus and the equatorial surface is established early in the mitotic cycle and remains unchanged. In order to learn more about the process by which the mitotic apparatus establishes the division mechanism, regions of cleaving echinoderm eggs (Echinarachnius parma, Lytechinus pictus) were continually agitated or stretched while establishment took place. Normal cleavage occurred despite stroking and vibration of the equatorial surface at different frequencies. Cells continually stretched at right angles to the future cleavage plane produced temporally and morphologically normal furrows. Subsurface cytoplasm was agitated by moving the mitotic apparatus back and forth parallel to its axis and by a vibrating needle inserted between the mitotic apparatus and the equatorial margin of flattened cells. Neither of these operations blocked cleavage. Cells held and shaped by the nozzle of a pipette were pierced by a needle inserted through the polar surface and into the zone between the mitotic apparatus and the equatorial surface. The needle was then swept around the entire mitotic apparatus. Furrows developed in these cells; they appeared later than in controls and did not appear completely normal. Furrow establishment does not seem to depend upon a precise, long‐standing, stable arrangement of sub‐surface cytoplasmic components.