ON THE FATE OF THE BLASTOPORE IN THE NEWT. 659 



On the Fate of the Blastopore and the Presence 

 of a Primitive Streak in the Newt (Triton 

 cristatus). 



By 



Alice Jobiison, 



Demonstrator of Biology, Newnham College, Cambridge. 



"With Plate XLIV. 



The coincidence of the blastopore with the anus in the Newt 

 has already been observed by Mr. Sedgwick.^ His assertion 

 was, he says, based only upon surface views. He therefore 

 suggested to me that I should attempt to verify it by cutting 

 sections of the embryos, and my results confirm what he has 

 stated." 



I. The Fate of the Blastopore. 



A. At the close of segmentation the blastopore is placed in 



the normal position at the hind end of the embryo. With the 

 greater growth of the dorsal surface, consequent on the appear- 

 ance of the medullary folds and formation of the medullary canal, 

 it comes to occupy a place on the ventral surface at some distance 

 from the hind end (vide fig. 11). Its distance from the hind end 

 increases as development goes on (vide figs. 12, 13). The tail 



1 A. Sedgwick, " On the Origin of Metameric Segmentation and some other 

 Morphological Questions," this Journal, January, 1884. 



2 Some of the main points of this paper have already appeared in a com- 

 munication made to the Royal Society in June, 1884. 



