52 THE ANCESTRY OF VERTEBRATES 



to the solution of this divergence of opinions in studying 

 the relation of the anus to the blastopore, my attention was 

 drawn to the different ways in which in Anurans (Rana 

 esculenta) and Urodelans (Amblystoma tigrinum) the cerebral 

 plate closes. In the former there may be noted quite distinctly 

 a growing up of the transverse cerebral fold, a process 

 which, at the closure of the brain vesicle, plays an equally 

 important role as the growing over of the lateral cere- 

 bral folds (Fig. 3 of the plate). In fig. 5 the neuropore is repre- 

 sented, apparently for the first time in Anurans. At least 

 V. KUPFFER (1906) in HertwiG's Handbuch says concerning 

 the Anurans: "Der Neuroporus ist im letzten Momente 

 vor seinem Schlusse noch nicht zur Beobachtung gekommen," 

 nor is there in investigations of later date anything to be 

 found on this subject. From the situation of the recessus 

 neuroporicus in median sections of later stages V. KUPFFER 

 corcludes: "Es haben sich wohl die Rander des Neuro- 

 porus bei Einleitung des Schlusses einwarts gerollt und 

 damit die Hirnwand zuriickgelagert". The result is a dorsal 

 neuropore, corresponding in its situation to Hatschek's 

 "angular" neuropore and confirming V. KUPFFER's views, 

 since it denotes the anterior end of the dorsal suture, which 

 does not continue in front of it. 



As a rule an open neuropore seems not to occur, the 

 fusion of the medullary folds being performed over their 

 whole length nearly simultaneously, or, in any case, to 

 have a very short-lived existence. At least in many other 

 longitudinal series of similar stages I did not find it. 



These processes are entirely different in the Axolotl. Here 

 there is hardly any question of a growing up of the transverse 

 cerebral fold. The closure of the cerebral plate is exclusively 

 performed by the growing up and the median fusion of 

 the lateral folds. An open neuropore was not found, but an 

 examination of complete eggs and sections shows conclusi- 

 vely, that the anterior end of the dorsal suture, corresponding 

 to the place of the neuropore, is here situated terminally, 

 just as in Petromyzon. The whole praechordal brain 

 vesicle, as shown by a comparison of fig 7 and 8 of 

 the plate, has in the axolotl a much more elongated shape 

 and much more the character of a tube 



The animal pole not a fixed point? — Thus we see in 

 two closely related groups the closure of the cerebral 

 plate being performed in entirely different ways. For the 



