. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 410 BULLETIN OF THE the whole animal kingdom the 'egg nucleus' of the mature egg capable of being fecundated arises from the dot of the germinative vesicle which [latter] is ; In a paper on the development of fresh-water pulmonates, Rabl ('75, pp. 197, 198, 223) adopts Haeckel's view of the phylogenetic significance of the disappearance of the germinative vesicle; namely, that it is evi- dence that the earliest ancestors of the Gasteropoda, as of all other living- organisms, were of the simples
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 410 BULLETIN OF THE the whole animal kingdom the 'egg nucleus' of the mature egg capable of being fecundated arises from the dot of the germinative vesicle which [latter] is ; In a paper on the development of fresh-water pulmonates, Rabl ('75, pp. 197, 198, 223) adopts Haeckel's view of the phylogenetic significance of the disappearance of the germinative vesicle; namely, that it is evi- dence that the earliest ancestors of the Gasteropoda, as of all other living- organisms, were of the simplest possible structure. The polar globules emerge from the yolk on account of its contractions during the first seg- mentation, and are usually two in number, the first one being the larger. Kabl entertains peculiar ideas concerning their physiological signification. Since, after a period of quiet, they are uppermost, he concludes that the pole at which they appear is the specifically lightest part of the egg, and that it is safe to assume, inasmuch as they are thus interposed between the egg and the envelope of the albumen, that their function is to protect the egg from pressure. For this reason one must consider these struc- tures protective organs of the embryo acquired through adaptation to the method of unequal segmentation. In Helix at the time of the disappearance of the germinative vesicle, or soon after, there emerge from the yolk, according to Von Jhering ('75, pp. 303, 304), from one to three polar globules. Whether the vesicle simply perishes, or is ejected, whether or no there is a connection be- tween it and the polar globules, cannot be determined on eggs so unfa- vorable for study. The formation of the globules is proof for the author . of the existence of a vitelline membrane (Taf. XVII. Fig. 2. d). •Without contributing any personal observations which bear immedi- ately on the early stages of the egg, Haeckel ('75, pp. 421, 426, 434, 435, 446, 480-483) utilize
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