ox THE tiASTRULATlON IN I'ETKOMYZON. 21 



inöii;lit uliirh is expressed in (his sliori account; indeed, lie 

 coiTcctly uhserved tlie position at wliicli the blastopore becomes 

 lirst visiblr. Aeeordiiii;- to liini, it is Ibiind "/wischen dem Kande 

 der Keindiöhle und dem ( !e,i;en})ol," wlule all other investigators 

 maintain that the ])()re oeeiir.s at the boundary between the 

 mieromerie and the macromeric part, /. c, at the junction-bnc 

 itself. This part — the part of the first appearance of the 

 blastoi)ore — is, however, not regarded by Goette, as 1 do, as a. 

 maeromerie part, but as a mieromerie ; for, according to him, 

 the conical eminence is brought about by " Anbiiufung der dort 

 scheinbar entstehenden und hinabrückenden Mikromeren,"^' and 

 the blastoporic cavity is nothing else than a fissure appearing in 

 this cell-mass. Starting from this standpoint, he assumes that 

 the Nvhole process of gastrulation consists in two processes : a) the 

 backward shifting of the mieromerie layer roofing the segmenta- 

 tion cavity and the forward pushing of the layer forming the 

 archenteric roof, which 1)oth represent his so-called '' dorsale 

 Einstülpung," and /;) " Umwachsung der Makromeren durch die 

 Mikromeren." The process which brings forth the "Anhäu- 

 fung " of the micromeres represents, according to Goette, this 

 backward shifting of the mieromerie roof of the segmentation 

 cavity. This assumption is, I believe, not in accordance 

 with the facts, and the point of dispute lies after all in the 

 origin of the cells giving rise to the " Anhäufung " or the conical 

 eminence. 



There are several facts which make us infer their being 

 macromeric in origin. First of all, these cells are loaded with 

 thickly-crowded yolk-granules and contain large nuclei, so that 

 they can not be distinguished, in these respects, from those in 



1) lac cil; \}. 4. 



