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Joined 2026-09-21 Message
Raymond Rappaport Created 2026-10-18 Updated 2026-11-05
Researcher in cytokinesis. Rappaport manipulated sand-dollar eggs to investigate the cleavage stimulus, using altered cellular geometry to test how division machinery determines the position of a furrow.[ref]
Experiments concerning the cleavage stimulus in sand dollar eggs by Raymond Rappaport. Title, author list and reported study
Toroidal sand dollar egg experiment 2026-10-18
In 1961, Raymond Rappaport gently removed membrane and jelly from sand dollar ova with a constricted pipette. After fertilization, he used an inverted optical microscope and rack-and-pinion manipulator to press a needle-mounted glass sphere through an egg onto the chamber floor, producing a torus-shaped biological cell. Visible spindle apparatus positions and cleavage furrow progression were the readout.[ref]
Experiments concerning the cleavage stimulus in sand dollar eggs by Raymond Rappaport. Experiments concerning the cleavage stimulus in sand dollar eggs, pp. 81–82, Materials and Methods: egg preparation, inverted microscope and sphere manipulation
First cytokinesis opened one side into a horseshoe containing two cell nuclei. During the next division, daughters separated from its free ends; an additional cleavage furrow crossed between mitotic asters of different spindle apparatuses. Control eggs supplied the timing comparison. This region lacked intervening chromosomes or a previous nearby spindle apparatus. This supported mitotic aster-associated positioning, without identifying the signal or establishing universal necessity.[ref]
Experiments concerning the cleavage stimulus in sand dollar eggs by Raymond Rappaport. pp. 81–82, introductory experiment summary, Results §1 and Figure 1 legend: horseshoe, second division, control comparison and furrowing between separate mitotic figures
Manipulation and inference in the toroidal sand dollar egg experiment
. Original apparatus and logic schematic; mitotic aster rays are symbolic. Details.