. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. THE CELL ORIGIN OF THE PROTOTROCH. II5. Fig. 3. — Loxodromic curve (" left-handed spiral ") described about a sphere, showing the general direction of the cleavage furrows which cut the cells of the 2-, S-, and 32-cell stages. size of the resulting blastomeres, yet the irregularity is not so great as to obscure the rhythm of cleavage, which expresses itself in the following manner: Each of the two cells divides, so that we have a 4-cell stage ; then each of these cells divides, and so o
. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. THE CELL ORIGIN OF THE PROTOTROCH. II5. Fig. 3. — Loxodromic curve (" left-handed spiral ") described about a sphere, showing the general direction of the cleavage furrows which cut the cells of the 2-, S-, and 32-cell stages. size of the resulting blastomeres, yet the irregularity is not so great as to obscure the rhythm of cleavage, which expresses itself in the following manner: Each of the two cells divides, so that we have a 4-cell stage ; then each of these cells divides, and so on, the number of cells increasing in geometrical progression until the egg consists of sixty-four cells. A distinct rhythm is ob- served also in the direc- tion of cleavage, for the cleavage planes lie ob- liquely across the meridians of the Q^g. The cells in the 2-, 8-, and 32-cell stages are divided by cleavage furrows which take the general direction of the loxodromic curve in Fig. 3,^ which may be rather loosely but conveniently defined as a left-handed spiral described around a sphere from pole to pole. The cells of alternate gen- erations, namely, of the 4- and i6-cell stages, are cut by furrows which have an opposite direction, as rep- resented in Fig. 4. These curves may be called, for convenience, left and right respectively, following the conventional nomen- FiG. 4—Loxodromic curve ("right-handed spiral"), claturC for thc thrCads OU having the general direction of the furrows which cut the 4- and i6-cell stages and many of those of the 64- 3- SCrCW. cell stage. Xhc rhythm of division 1 In the diagram this curve cuts the equator at one point only. The curve will, of course, cut the equator at any point, if Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Marine Biological Labo
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