296 HELEN DEAN KING. 



investigation of the early development of Rana, is in part as 

 follows : " Bei clen Anuren liegen insofern anderen Verhaltnisse 

 vor, also hier die Zellen, welche die dorsale Wand des Darmes 

 bilden, von Anfano; an vorhanden sind ale eine Zellenreihe und 



CD 



zwar als eine untere Zellenreihe jener Anlage, aus welcher die 

 Chorda entsteht." Lwoff and I are therefore in accord in 

 believing that in Rana there is no upward growth of the yolk 

 cells from the lateral walls of the archenteron to form the 

 mid-dorsal wall. 



There is great diversity of opinion concerning the manner 

 of the formation of the notochord in the Anura ; and, consider- 

 ing the careful work that has been done in this line, it seems 

 highly probable that the process is not as uniform in this group 

 as it is in the Urodela. 



Goette (6), from his study of the development of Bombinator 

 igncns concludes that in this species a central chord of meso- 

 blast in the mid-dorsal region of the embryo separates from the 

 two lateral sheets to form the notochord. This view is supported 

 by the later investigations of Schultze (18), and Morgan (15) 

 who worked on different species of Rana. 



In a paper on the development of the middle germ layer in 

 Rana temporaria, Hertwig (8) gives a number of figures of the 

 posterior part of the embryo that bear a striking resemblance to 

 those I have drawn of a similar region in the embryo of Bnfo 

 lcnti-inosiis. Hertwig believes, however, that the entire noto- 



cj O 



chord in the Anura as well as in the Urodela, is derived from a 

 chorda-entoblast which at the sides of the archenteron pass into 

 the endoderm cells forming the lateral walls. Field (5), from 

 his investigations on Rana temporaria and on Bnfo vulgaris, 

 agrees with Hertwig regarding the manner of formation of the 

 notochord, as do Robinson and Assheton (17) who worked on 

 Rana temporaria. Balfour (i) also inclines to the same opinion, 

 although he states that his evidence for so doing is not entirely 

 conclusive. 



As a result of his study of the early development of Bombina- 

 tor igncns, Perenyi ( 1 6) advances still another theory regarding 

 the formation of the notochord. He states that, when the blas- 

 topore closes in, " die vertikal nach innen vordringenclen Zellen 



