398 T. n. MORGAN AND VMi TSUDA. 



In these figures I believe Roux represents the early embryo 

 as extending over too great an extent of surface of the sphere. 

 Moreover, it seems, as I have said, most probable that the 

 blastopore does not start at the equator of the egg, but some 

 distance below that circle. 



Schultze's conclusion that the embryo lies over the black 

 hemisphere may be dismissed, as it is completely contradicted 

 by well-determined facts. 



Finally, Robinson and Assheton make certain statements as 

 to the method of closure of the blastopore that call for notice. 

 Apparently at the outset they have orientated the embryo 

 wrongly, for they state, '^ The segmentation cavity has a roof 

 which ultimately becomes the anterior wall of the gastrula ; 

 for the anus, which marks the posterior end of the embryo, 

 appears at the opposite pole of the ovum, — that is, in the floor of 

 the segmentation cavity." Again, they say, '' For during the 

 formation of the blastopore the epiblast does not grow over the 

 yolk-cells enclosing them by a process of embolic invagination." 

 This statement is intended to apply rather to the extension of 

 the epiblast over the sides of the embryo, and as such is per- 

 fectly correct. But, in addition to this process of delamina- 

 tion, there is a decided and extensive overgrowth, as we have 

 seen, of the dorsal lip of the blastopore enclosing the yolk em- 

 bolically. Further, the statement of Robinson and Assheton 

 that no portion of the archenteron in the anura is formed by 

 invagination is certainly incorrect, as I hope to show in a later 

 paper. 



They continue, " According to some former accounts, to 

 which we have made reference above, the anus of Rusconi has 

 been said to diminish in size by the gradual coming together 

 of each portion of the blastoporic rim simultaneously. This 

 we believe to be incorrect. The anus of Rusconi gradually 

 diminishes in size by the concrescence of the ventral part of 

 the lateral lips." In their diagrams, to show the method by 

 which the ventral lip of the blastopore comes together, they 

 show the right and left sides applied to one another, and sub- 

 sequently fused. Later they say, " We infer .... that the 



