224 RICHARD ASSHETON. 



for invagination is, to say the least, inconclusive;" and on the 

 other hand (p. 332), " There is not a shred of evidence to show 

 that the large cells at first surrounding the mouth of the blas- 

 topore are not subsequently pushed in by the ingrowth of 

 ectoblast cells. No positive evidence whatever exists to prove 

 either the impossibility of invagination or the likelihood of no 

 invagination. I find it difficult to gather the reasons that 

 have influenced Houssay and Robinson and Assheton to adopt 

 the view that invagination does not occur.'' 



Jordan then describes (pp. 333-4) "ocular evidence that 

 the small cells around the lips of the blastopore are actually 

 infolded." 



Morgan, after a description of interesting experiments after 

 the method of Roux upon the living egg, says, " 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.'' 



Of course this latter statement must depend upon the exact 

 meaning to be attached to the word archenteron. 



My own conception of the term archenteron is that cavity 

 which in the embryo is supposed to represent the digestive 

 cavity of a hypothetical ancestral " gastrula," no matter how 

 this cavity was brought about. 



If, however, by archenteron is meant any subsequent pro- 

 longation of this cavity, such as would represent a post-gastrula 

 condition ancestrally, then certainly such a statement was 

 inaccurate. 



When Dr. Robinson and I made the statement referred to, 

 we regarded as archenteron part of the cavity which I now con- 

 sider to represent a post-gastrula condition. In other words, 

 I agree with Morgan and others to a certain extent as regards 

 the growth over of the dorsal lip of the blastopore, and consider 

 only the most anterior part of the gut cavity of the frog's 

 embryo at the time of the closure of the blastopore as being 

 formed by a splitting, and as representing the true archenteron. 



Accordingly, in my opinion, the sentence (referred to above) 

 by itself accurately describes the facts, but in the context in 



