CYTO-EMBRYOLOGICAL STUDIES OF SEA URCHINS. I. THE MEANS OF FIXATION OF THE MUTUAL POSITIONS AMONG THE BLASTOMERES OF SEA URCHIN LARVAE

¹ Biology Department, Tokyo Metropolitan University, Meguro-Ku, Tokyo, and Misaki Marine Biological Station, Misaki, Kanagawa-Ken, Japan

1. The proposal made by the Andrews and A. R. Moore that sea urchin blastomeres are bound together by means of protoplasmic strands is rejected and the notion is advocated that sea urchin blastomeres are stuck to the inside surface of the hyaline plasma layer by attachment fibers radiating out from the blastomere surface. This mode of fixation secures definite relative positions among the blastomeres. Evidences are put forward indicating the above relation.

2. Possible sources of errors in the spinning theory of Andrews and Moore are analyzed.

3. Points concerning the movement of the cell surface during cleavage and the pattern of cleavage are considered.

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