500 BULLETIN OF THE 



micropyle, or " Dotterhiigel," cannot yet be decided. He says he has 

 sometimes seen its rotation through 90° of arc, and adds, that " there- 

 fore, since the spermatozoon as a rule penetrates at the ' Dotterhiigel,' 

 the first plane of division passes through that point (Dotterhiigel). 

 But inasmuch as the latter also indicates the place where the directive 

 corpuscles emerged, one may also say that the first segmentation plane 

 generally coincides with the radius which is determined by the long 

 axis of the nuclear spindle or by the course along which the directive 

 corpuscles emerge." "But," he adds, "it is not to be forgotten that 

 the spermatic element may also penetrate at other places than at the Dot- 

 terhiigel, and that then, not the ' Mikropylenhiigel,' but the radius along 

 which the spermatozoon has penetrated would determine the direction of the 

 first cleavage planed 



Resting on this argument, Selenka claims that it is not right to con- 

 sider that part of the yolk where the directive corpuscles emerge the 

 formative pole, and therefore that the name polar globules is not suit- 

 able for the directive cells of Toxopneustes. 



I believe that Selenka is in error in saying that the plane of cleavage 

 is determined by the line along which the spermatazoon penetrates, 

 and think the protuberance called Dotterhiigel may be the source of 

 the difficulty. This the author has defined as the elevation left at the 

 place where the directive corpuscles escaped. He has doubtless ob- 

 served cases in which the first cleavage plane did not pass through this 

 elevation, and hence concludes there is not a constant relation between 

 the position of this plane and the place where the polar globules emerge. 

 Unless the identity of the Dotterhiigel and this place of emergence are 

 indisputably established, his conclusions will not necessarily follow from 

 his observations. 



I do not see that that there is any conclusive evidence that the 

 " Dotterhiigel " may not be some other protuberance of the yolk than 

 that which was left behind by the polar globules ; for example, such 

 an elevation as Giard has called the second cumulus, and which Fol 

 has affirmed to be a projection of the yolk into a place of the 

 oolemma corresponding to the point of the egg's ovarian attachment. 

 That this may really be the case here seems none the less probable 

 from the remark which Selenka (p. 6) himself makes, to the eff'ect that 

 "the spermatozoa seem to penetrate the gelatinous mantle preferably 

 in the immediate vicinity of the ' Dotterhiigel,' and that this is appar- 

 ently a more practicable passage, — it may be on account of the emer- 

 gence of the polar globules at this point, it may be because it is at 



