172 ALICE JOHNSON. 



175, 176). In Salensky's^ account, however, no such structure 

 as a primitive groove is mentioned or figured. 



The solid condition of the hind end of the medullary canal, 

 such as I find in the Newt, has been described by StrahP for 

 the Lizard, and by Gasser' for the Bird. 



III. Summary of Facts and General Considerations. , 



In the Newt (1) the anus of Rusconi, or blastopore, becomes 

 the actual anus of the adult. 



(2) A primitive streak exists on the dorsal surface in front 

 of the open blastopore. 



(3) The primitive groove extends along the whole of the 

 dorsal surface from the open blastopore, and for a short dis- 

 tance in front of the medullary folds. 



(4) The front end of the primitive groove deepens into a 

 distinct pit, at the apex of which there is, almost certainly, a 

 fusion between the hypoblast and epiblast. 



The Newt affords another instance of the variability of 

 position of the last open part of the blastopore in different 

 groups of the Chordata. 



In Amphioxus, the blastopore is posterior, and gives rise to 

 a neureuteric canal on the formation of the medullary folds 

 and closure of the medullary canal. 



The same is the case with the Ascidians. In Elasmobranchs, 

 the blastopore is converted into a neurenteric canal on the 

 closure of the medullary folds. Behind this, there is a yolk 

 blastopore, which closes without leaving a trace. 



No neurenteric canal is known in Teleosteans, and an 

 invagination, giving rise to a blastopore, has not been de- 

 scribed. 



' W. Salensky, " Recherches sur le developpement du Sterlet," 'Archives 

 de Biologie,' vol. ii, 1881. 



^ H. Strahl, "Beitrage zur Entwicklung von Lacerta agilis," ' Arch, f 

 Anat. u. Phys.,' 1882. 



' Gasser, " Der Primitivstreifen bei Vogelembrjonen," ' Schriften d. Gesell. 

 zur Beford. d. gesammten Naturwiss. zu Marburg,' vol. ii, supplement i 1879. 



