. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CELL SURFACE BEHAVIOR DURING CLEAVAGE 499 sion. Quoting him: " In short, the new cell boundaries are not formed in the calcium-free sea water in the course of the early cleavages. The surface of each blastomere is covered by the extension of the pigmented cortical cytoplasm. But, when the blastomere is replaced in the normal sea water, it regains the capacity of forming the new cell boundaries. In this case the blastomere is able to form the pluteus. When the egg is cultured successively in calcium-free sea water, no fo
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CELL SURFACE BEHAVIOR DURING CLEAVAGE 499 sion. Quoting him: " In short, the new cell boundaries are not formed in the calcium-free sea water in the course of the early cleavages. The surface of each blastomere is covered by the extension of the pigmented cortical cytoplasm. But, when the blastomere is replaced in the normal sea water, it regains the capacity of forming the new cell boundaries. In this case the blastomere is able to form the pluteus. When the egg is cultured successively in calcium-free sea water, no formation of the embryo in it is possible. In this case the distribution of the pigment granules is irregular" (p. 239). From this description, he apparently missed the formation of new surface in Ca-free sea water entirely. In the authors' experience, in order to observe the formation of new surface, special precautions are necessary to secure a good condition of the cultures. Overheating of the preparation by the light source or a slight shortage in the quantity of the culture medium at the time of observation immediately impairs the eggs. During the first cleavage, when such injury occurs, the eggs invariably stop their development at the stage in which the separation of the blastomeres is just completed and the granules are accumulated at the sides of the furrow (Plate II, A-3, A-4). Therefore, even as early as the beginning of the inter- kinetic period, it is possible to predict whether or not an egg under observation will undergo further cleavages. Cultures were encountered, especially towrard the end of the season, in which all the eggs remained in this state. In such eggs, the granules sooner or later begin to clump together irregularly, and the eggs finally die. But so far as the authors are aware, as long as the condition of the egg remains favorable, each cleavage is regularly followed by the formation of new surface. Hence, it is impossible to accept Motomura's a
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
