334 JORDAN. [Vol. VIII. 



the parts played by each. Epibole and embole certainly run 

 into each other at the lip of the blastopore, and I see no reason 

 for supposing that the process of cell proliferation, which is so 

 active in the exterior cells, ceases when the cells have been 

 engulfed by the epibolic overgrowth. Of the existence of the 

 latter process there can be no question. Two hours spent in 

 watching the marginal blastoporic cells in the living amphibian 

 egg will enable any one to determine this to his complete 

 satisfaction. 



VI. Fate of the Blastopore. 



It is with some diffidence that I take up the question of the 

 fate of the blastopore, since for a long time the literature on 

 the amphibian blastopore has been increasing in quantity if 

 not in cogency. It would be a superfluous task to review 

 in cxtcnso the far from concurrent opinions, since an excellent 

 summary of the literature has been quite recently given by 

 Erlanger ('89), and by Robinson and Assheton ('9i), to mention 

 only two of the most recent. ^ On one point only is there 

 practical agreement among all the later investigators, namely 

 that the amphibian anus is either a remnant of the blastopore 

 opening, or a breaking through in that region of the embryo at 

 one time occupied by the blastopore. Whether it is in all 

 cases a persisting portion of the original blastopore, or is in 

 some cases a new opening of the old blastopore raphe, is, how- 

 ever, a much disputed question. 



It seems necessary for the sake of clearness, if for no other 

 reason, to distinguish between the Anuran and Urodelan 

 blastopore. There seems good cause to suspect that the 

 phenomena attending the closure of the blastopore differ in 

 the two groups ; at any rate, nothing is to be gained by a 

 hostile criticism of the results obtained from the study of one 

 group upon the basis of results obtained from the study of the 

 other. 



^ It seems a curious oversight on the part of Robinson and Assheton that they 

 make no mention either of Ilertwig's papers (Jenaische Zeitschr f. Naturwiss., 

 1882 and 1S83), or of Schanz's (Jenaische Zeitschr, 1887), since these papers must 

 be regarded as among the most important contributions to the literature of the 

 blastopore (cf, Erlanger, '91). 



