236 HUBERT DANA GOODALE 



Other observers deny any form of concrescence. One group, 

 of whom Jordan ('93) appears to have been the first, followed by 

 Ej'cleshymer ('95) and Kopsch ('95), holds that the blastopore 

 is formed by convergence. By this they mean that part at least 

 of the material which lay about the egg in a ring moves towards 

 a central point, the lower pole, along the meridians of the egg, 

 that is, at right angles to the direction described by the two groups 

 of authors mentioned above. As a consequence of this movement 

 it must become spread out over the lower hemisphere of the 

 egg. Out of what may be called the anterior half of the ring, 

 more or less (according to the species) , the posterior part of the 

 embryo develops. 



There is still another group of observers, e. g., Assheton, who 

 believe that the posterior part of the embryo is formed by over- 

 growth. I understand by this term that the material out of 

 which the posterior part of the embryo is formed, lies in the dorsal 

 lip of the blastopore, and as the lip moves downwards, it spreads 

 out into a plate. I judge, that, according to this view, the lateral 

 edges of the posterior part of the neural region, move downward 

 in lines roughly parallel to each other. 



Jordan appears to have reached his conclusions from general 

 observations. Kopsch's brilliant work was the first experimental 

 proof adduced in its support. My own work confirms Kopsch's 

 results, although owing to the specialized mode of blastopore 

 closure in Spelerpes, they are slightly modified. If there were 

 any concrescence, even of the posterior parts of the embrj^o, the 

 marks should have moved approximately at right angles to the 

 course they actually took. The pumerous pricking experiments 

 that have been made on the blastopore of the frog support the 

 view of convergence in a remarkable way, although they have 

 commonly been interpreted in support, in some form or other, 

 of the concrescence theory. Miss King ('02) has made an ex- 

 tended series of these experiments. If a slight exovate be made 

 near the edge of the blastopore in any section, it is later found at 

 the posterior end of the embryo. If the exovate is made a little 

 further above the edge it remains stationary. If, instead of a 

 puncture, a mark had been made with Nile blue sulphate, I 



