FATE OP BLASTOPORE, ETC., IX CHELOXIA. H 



in Contrilnition JT. of the present «eries,* I decided to follow the 

 fate of the cell-mass which Isiiikawa and myself have homologised 

 with the yolk-plug- of Amphihia. The results obtained are beyond my 

 expectations. I have been able to elucidate a series of ficts, hitherto 

 entirely unnoted, which seem to throw a ß-reat deal of lioht, not onlv 

 on the cell-mass in question, but on the nature of the primitive streak 

 and on the formation of the posterior end of the embryo. In con- 

 secpieuce, I believe that the nature of the meroblastic amniote egg is 

 made much clearer than heretofore, and that important conclusions 

 can be drawn in regard to it. 



My observations have been extended over three species of Chelonia, 

 viz : — Trionijx jajjonicns, Clômmijs japouica^ and Chelonia caouana. 

 The materials used were the embryos of Chelonia collected, as re- 

 counted in Contrib. Jf'.,* in the province of Tötömi, and those of 

 Tnonijx and Clemnijis preserved from the more than abundant supply 

 at the Hattoei turtle-farm in Fukagawa, Tokyo. It is scarcely 

 necessary for me to point out the great advantage of making a com- 

 parative study of nearly allied forms : observations on one species 

 often throw a flood of light on points in other species which would 

 otherwise remain inexplicable and obscure. In the present case, if 

 I had had only the Trioni/x embryos, I should probably not have 

 succeeded, or at an}^ rate should have had a great deal of difficulty 

 in making out the course of development given in the following 

 pages, while that species is indispensable in pointing out how the 

 story so plain in the other two species has come to be abbreviated in 

 hiofher forms. 



lîefore ]3roceeding further, it may perhaps be well to re- 



* See tlie list at the end of the article. 



