STUDIES ON UNEQUAL CLEAVAGE IN SEA URCHINS I. MIGRATION OF THE NUCLEI TO THE VEGETAL POLE |
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| Authors: | KATSUMA DAN |
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| Affiliation: | Francisco Villa, 19-8, 3-chome Kamiyoga, Selagaya-ku, Tokyo 158 and Misaki Marine Biological Station, Koajiro, Miura-shi 238–02, Japan |
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| Abstract: | It has been known for nearly a century that at the 16-cell stage of sea urchin embryos, the animal 4 cells divide equally and horizontally, whereas the vegetal 4 cells cleave unequally and practically vertically into macromeres and micromeres. Recently, more careful observations were made on the process of micromere formation and it has been revealed that a primary cause for the inequality lies in the migration of the 4 vegetal nuclei to the vegetal pole of the embryo which brings about excentricity of the mitotic apparatus. Records of this phenomenon are given in the present paper. |
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