. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 2'20r 5'lOr. o 8'35" FIGURE 14. Combination of a median and a polar hole. Notice that the polar hole is not affected at all. The behavior of the median vegetal hole remains unchanged by the presence of the polar hole. Now, if the astral rays of the vegetal region were rigid enough, this condition would immediately cause a fission in the vegetal region between the two asters as in the case of the Astriclypeus eggs. But, actually, the vegetal portion of Spirocodon eggs is much more fluid and more deformable. Therefore, in
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 2'20r 5'lOr. o 8'35" FIGURE 14. Combination of a median and a polar hole. Notice that the polar hole is not affected at all. The behavior of the median vegetal hole remains unchanged by the presence of the polar hole. Now, if the astral rays of the vegetal region were rigid enough, this condition would immediately cause a fission in the vegetal region between the two asters as in the case of the Astriclypeus eggs. But, actually, the vegetal portion of Spirocodon eggs is much more fluid and more deformable. Therefore, instead of tearing the vegetal cortex apart (as in typical furrow formation) the cortex and the rays are both stretched out, allowing the central parts of the asters to rotate. In other words, in Astriclypeus, the annulment of the strain exerted by the elongating spindle is achieved by the breaking of the cortical layer (furrow formation) while in Spiroco- don it is accomplished by the yielding of the cortex and the rays to the strain (with- out furrow formation). What the authors think about the condition of the rays and the cortex is shown diagrammatically in Figure 16. The cleavage stage corresponds to stage B of Plate II. The thin lines represent extremely stretched parts of the rays and of the cortex while the thick ones are the parts which are stretched slightly or not at all. According to our interpretation, there are no rays which go to the furrow side. This ray-free narrow strip lining the furrow side must correspond to the "fan- shaped ray-free area" described in connection with Astriclypeus eggs (Dan and Dan, 1947). (In Astriclypeus eggs, as the median crossing rays are caught by the. 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 Laboratory (Woods Hole, Mass. ); Marine
Size: 1867px × 1339px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
