L884.] The Changes in the Blastopore of the Newt. 65 



the axis which bears it. This may be shown simply in tabular 

 form thus 



Shoot. 



Axis. Leaf. 



Phyllopodium. Pinna. 



III. " On the Changes and ultimate Fate of the Blastopore in 

 the Newt (Triton cristatus)" By ALICE JOHNSON, Newnham 

 College, Cambridge. Communicated by Professor MICHAEL 

 FOSTER, Sec. R.S. Received May 15, 1884. 



In a paper lately published on "The Origin of Metameric Seg- 

 mentation," Mr. Sedgwick mentions that he was led to conclude 

 from surface views of a large number of stages that the blastopore 

 of the newt (Triton cristatus) does not close, but persists as the anus. 

 He suggested to me afterwards that I should attempt to test this 

 observation by cutting sections of the embryos, and my results fully 

 confirm what he previously stated. 



Scott and Osborn, in their account of the development of the 

 newt, describe a posterior dilatation of the medullary canal, the sinus 

 rhomboidalis, which remains open for some time after the rest of 

 the canal has closed. They say that its folds enclose the blastopore, 

 and that, therefore, when they come together, a neurenteric canal is 

 formed. Their account of the exact date of the closure of the 

 medullary folds in this region is a little obscure, but seems to 

 indicate that the event takes place while the number of protovertebree 

 is quite small, and before the rudiments of the visceral arches and 

 tail have appeared. 



Hertwig figures an open blastopore at a slightly later stage than 

 this, but, judging from his surface views of the embryo, it is situated 

 at the hind end of the tail. 



At a stage when the medullary folds are widely apart, the slightly 

 elongated blastopore is placed at the hind end of the body. While 

 the folds are approaching one another the dorsal surface grows faster 

 than the ventral, so that the blastopore is carried round on to the 

 ventral surface. When the folds have completely coalesced, and 

 before there is any trace of a tail, the blastopore is placed at some 

 little distance from the hind end, which is much swollen and spherical 

 in outline. 



In transverse sections of the stage just described we find the blasto- 

 pore actually communicating with a cavity in the midst of the yolk- 

 cells. This cavity is so exceedingly narrow that it can hardly be 



VOL. XXXY1I. F 



