76 K. MITSUKURI; 



writers, the neurenteric canal itself is included with the blastopore, 

 but this is a part of the original archenteron, and we must consider its 

 dorsal opcniiuj alone as a part of the blastopore. It is highly signiiicant 

 that in such an advanced stage as that represented by Series IX or Fig. 

 8, the hindmost part of the neurenteric canal is open dorsally 

 (sect. <j) and becomes continuous with the groove which forms the 

 second part of the Ijlastopore. Of this second part, there is notliing 

 special to say, since it so plainly is a part of the blastopore. In the 

 third part, the groove is found only around the anterior part of 

 the circumference of the yolk-plng, and I have never seen any visible 

 posterior boundary. This absence I believe, is due to tlie yolk-plug 

 being a rudimentary structure. 



Tlie line of cell-proliferation from the blastopore lips I have 

 called the pruiiitice strealc, and the groove lying on it in the median 

 line, the prluiitiec groove. 



In Cheloma and Clemmijs, the blastopore lips do not become 

 fused ; hence the primitive groove is distinct. In Trioni/x, the groove 

 is not present, but proliferation takes place all the same along the line 

 where the groove ought to l)e 



The anterior half of the primitive streak is much thicker than 

 the posterior half and gives rise to the mass known as the " End- 

 wulst.''' The posterior part i-emains thin to the end. The former 

 corresponds to the " vorderer dicker Theil (^ps. /.)," and the latter to 

 the "hinterer, dünner Theil {ps. II.),'' of Gasser ('78).* The 

 anterior thick part rises as the tail-sirelling. This is formed iDy the 

 addition of the new cell-mass on the dorsal surface, in other words by 

 iipheaval or elevation and not hij folding (Series X and XI). The 

 lateral plates of the mesoblast do not take part in this upheaval. 



* It is a great pleasure to find uiy results agreeing in many points with the lieautiful and 

 accurate description l>y this author. 



