. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CELL SURFACE DURING CLEAVAGE. VIII 183 (1) It was stated that as the imposed strain is equalized, during the latter half of the cleavage process, the vegetal material is shifted around toward the animal side and the spindle is shifted down. These coupled movements are an action and a reaction. As a result, the authors cannot agree with the opinion that a cleavage furrow strives to reach the opposite pole by its own power. Such an illusion must have arisen from the fact that when a cleaving medusan egg is observed, the only t
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CELL SURFACE DURING CLEAVAGE. VIII 183 (1) It was stated that as the imposed strain is equalized, during the latter half of the cleavage process, the vegetal material is shifted around toward the animal side and the spindle is shifted down. These coupled movements are an action and a reaction. As a result, the authors cannot agree with the opinion that a cleavage furrow strives to reach the opposite pole by its own power. Such an illusion must have arisen from the fact that when a cleaving medusan egg is observed, the only thing which can be seen moving is the cleavage furrow, and the cell body remains practically stationary. But this is due to a simple physical 'condition. When a cleaving medusan egg comes to lie on its side as the result of flattening, it must be resting on the substratum by two points, with the center of gravity of the cell somewhere on the line connecting these supporting FIGURE 16. The condition of the astral rays and the cortex as interpreted by the authors from stage B of Plate II. The distal portions of the vegetal rays are greatly stretched. The animal cortex is drawn into the furrow and the vegetal cortex is stretched to cover the lower half of the blastomeres. Greatly stretched parts are represented by thin lines. The ray-free area is spreading along the furrow wall. This figure is only a rough qualitative representation. Therefore, no matter what change occurs in the contour, as long as the center of gravity does not change its position, the cell cannot help remaining stationary. The rotational movement of the aster such as was discussed above will certainly not shift the position of the center of gravity very much. In other words, supporters of the opposing theory made an error in selecting the axes of coordinates. They took the more or less stationary cell contour as a reference and compared the movement of the furrow head with it. But if we have to choose a
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
