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 dissolved." 



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) utilizes the preponderating evidence in favor of 

 the disappearance of the germinative vesicle in support of his theory of 

 the palingenetic significance of the cytode stage of the egg, as a "Riick- 

 schlag der einzelligen Urform in die primordiale Stammform des Mo- 

 neres." If this atavistic return to the cytode condition should be 

 established for only a part of the animals, but fail for the remainder, 

 then the development in the latter cases would have to be considered as 

 a ccenogenetic process. 



LuDWiG ('75, p. 210) was unable to detect any such details in the 

 early stages of the egg of Chsetonotus as have been described by Auer- 

 bach and others, and therefore was only able to say that the germina- 

 tive vesicle disappears entirely while the jd\k undergoes contractile 

 changes. 



