ON THE FATE OP THE BLASTOPORE IN THE NEWT. 661 



Barabekei states that the blastopore disappears before the 

 formation of the medullary folds. 



As to the fate of the blastopore in other Amphibia, I con- 

 clude from ClarkeV account of the development of Ambly- 

 stoma that it becomes the anus in this form, though the fact 

 is not actually expressed in so many words. He says (p. 7), 

 " At the extreme anal end the (medullary) folds remain sepa- 

 rate over a small area, the space formerly occupied by the 

 vitelline plug (the mass of yolk-cells which projects into the 

 cavity of the blastopore and nearly fills it up at an earlier 

 stage), and form a rounded edge about this small cavity or 

 pit "(p. 8). " In a ventral view . . . are seen both the 

 optic vesicles . . . and the anus at the posterior end of 

 the neural tube " (p. 9). " The beginning of the tail also 

 shows distinctly, and its median ridge, at the end of which is 

 the dark cavity of the anus, is now much increased in size." 

 No mention is made of the closure of the blastopore, and 

 Clarke's figures (pi. ii, figs. 9, 10, 13, 14) confirm my deduc- 



tion. 



In Pelobates, Bambeke^ states that the anus appears to 

 him to correspond to the place formerly occupied by the 

 '^bouchon de Ecker " (vitelline plug). He figures it at a 

 comparatively early stage (vide plate iv, fig. 5). 



II. The Primitive Streak. 



A. — The first structure to appear on the surface of the ovum 

 after the segmentation has been completed is a groove which 

 generally extends from the blastopore along the greater part 

 of the dorsal surface. This is the " Riickenrinne " of the 

 German observers, the " Sillon median " or " Sillon primi- 



1 Ch. van Bambeke, " Nouvelles Recherches sur I'embryologie de3 Batra- 

 ciens," ' Archives de Biologic,' vol. i, 1880. 



2 S. F. Clarke, " Development of Amblystoma Punctatum," part i, external, 

 ' Studies from the Biological Laboratory of the Johns Hopkins University,' 

 No. 2, 1880. 



3 Ch. van Bambeke, " Recherches sur le Developpement du Pelobate 

 brun," • Memoires Couronnes, &c., de I'Acad. Roy. de Belgique,' 1868. 



VOL. XXIV. NEW SER. ^ ^ 



