Abstract
The movement of the protoplasm during cleavage was analyzed by tracing the movements of particles in the protoplasm by time-lapse microcinematography of the eggs of the heart-urchin, Clypeaster japonicus. Three methods of analysis are used. The first is to trace protoplasmic particles in the projected image frame by frame. The second is to record the displacements of protoplasmic particles at various regions of the egg within a definite period by printing several images of the same egg on the same sheet of photographic paper. The third is to record protoplasmic movement in the cleavage plane or along the spindle axis by projecting the film at a constant frame rate through a narrow slit on a sheet of photographic paper moving at a constant speed in a direction perpendicular to the slit. As a result of the analysis, which confirms the result of a previous study (Hiramoto, 1958), it is concluded that during cleavage of the sea urchin egg there is deformation of the preexisting cortex rather than the formation of a new cortex from endoplasmic materials.
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