ON THE FATE OP THE BLASTOPORE IN THE NEWT. 665 



B. Historical. — The great breadth and flatness of the 

 medullary plate at its first appearance is a well-known 

 characteristic of Amphibian embryos. They are further dis- 

 tinguished at this period from the embryos of other Vertebrates 

 by the division of the medullary plate into two symmetrical 

 halves by means of the dorsal or primitive groove. This 

 feature, as well as the continuity of the primitive groove with 

 the blastopore, has been noticed by almost all observers of 

 Amphibian embryology. Hertwig^ alone denies the continuity 

 of the two structures, but it has been described by Bambeke2 

 in Triton and Axolotl ; by Clarke-^ in Am.blystoma ; by 

 Ecker* in the Frog ; by Gotte^ in Bombinator ; and by Bam- 

 beke^ in Pelobates. Prevost and Dumas^ figure the primitive 

 groove in the middle of the medullary plate of the Frog, but 

 do not mention its blastopore. 



The only other Vertebrate, as far as I know, in which a 

 similar disproportionately broad medullary plate and a like 

 relation of the primitive groove to the medullary plate and 

 blastopore have been described, is the Sturgeon. Kowalevsky, 

 OwsjannikofF, and Wagner^ describe in the embryo Sturgeon 

 a specially broad medullary plate, in the middle of which is an 

 opaque streak, which they call the " Primitivstreif," though 

 they do not assert that any fusion of the layers exists there. 

 A " Primitivrinne " runs down the centre of the " Primi- 

 tivstreif," ending in the blastopore (vide their figures on pp. 



1 0. Hertwig, loc. cit. 



2 Ch, van Bambeke, " Nouvelles Recherches, &c,," loc. cit. 

 » S. F. Clarke, loc cit. 



* A. Ecker, "Icones Physiolog.," 1851—1859. 



5 A. Gotte, "Die Entwicklungsgeschichte der Unke," Leipzig, 1875. 



6 Ch. van Bambeke, " Recherches sur le developpement du Pelobate brun," 



loc. cit. 



7 Prevost and Dumas, " Deuxieme mem. s. I. generation. Developpement de 

 'oeuf des Batraciens," ' Ann. Sci. Nat.,' ii, 1824. 



8 A. Kowalevsky, Ph. Owsjanuikoff, and N. Wagner, " Die Entwicklung d. 

 Store," 'Vorlauf. Mittlieilung. Melanges Biologiques tires du Bulletin de 

 I'Acad.,' Imp., St. Petersbourg, vol. vii, 1870. 



