4G2 BULLETIN OF THE 



the pellucid spot is located. In from ten to fifteen minutes it is com- 

 pleted, leaving only a nipple-like protuberance from which the first polar 

 globule begins to emerge. " That part of the polar globule first to 

 appear is perfectly transparent, but the half last eliminated is filled with 

 minute, highly refractive granules, the outer border of which forms a 

 straight line at first." After its elimination, the yolk, which had re- 

 ceded from the vitelline membrane at the formative pole of the egg; 

 again fills out the perivitelline space coming in contact with the mem- 

 brane, and thus the polar globule is pushed so far back into the yolk 

 that it is seen with difficulty. A similar, but not so marked or regular, 

 peristaltic constriction accompanies the formation of the second polar 

 globule. In C. complanata the furrow often appears raised in the 

 middle, giving it the appearance of being double. It is possible that 

 the same phenomenon has been fixed by reagents in the Limax egg 

 shown in Fig. 55. 



The fate of the germinative vesicle and the significance of the polar 

 globules are discussed by Whitman at some length. The germinative 

 vesicle is not totally eliminated, so there is really no enuclear or cytode 

 stage, which, moreover, from a priori grounds could hardly be expected. 

 " Ontogeny furnishes numerous examples of reversion, but I believe no 

 case in which reversion is followed by progression to the same point 

 again." Although the genetic connection of the archiamphiaster and 

 the germinative vesicle were not absolutely demonstrated in Clepsine, 

 yet, granting this,- " the proof in Clepsine is as complete as it well can be 

 for opaque eggs that a part of the germinative vesicle persists as a nu- 

 clear element " (p. 34). 



The occurrence of polar globules the author thinks still a matter of 

 doubt in birds, reptiles, amphibians, most fishes, tunicates, arthropods, 

 and rotifers. I have shown it to be highly probable, however, that Stras- 

 burger has seen stages initiatory to the formation of a polar globule in 

 Phallusia. 



Whitman maintains that it is impossible to make a direct comparison 

 of the elimination of the entire germinative vesicle, as represented by 

 Balfour and Oellacher, with the formation of polar globules by amphias- 

 tral division. The " pole-cells " in insects, as they form the basis of the 

 sexual organs, cannot be equivalent to polar globules ; nor can the so- 

 called " testa-cells " of the ascidian egg. 



Perhaps the most interesting part of Whitman's discussion is that 

 which considers the historic origin of the polar globules (pp. 44 - 49), to 

 which the reader must be referred, since there is space here for only a 



