GASTRULATION AND EARLIEST DEVELOPMENT 199 



canal, as described by SCOTT and OSBORNE, was never 

 observed by her. SCHANZ (1887) in Triton punctatus comes 

 to the conclusion that the blastopore is constricted in 

 the middle, the anterior opening becoming the neuren- 

 teric canal, the posterior opening the anus. HOUSSAY 

 and BATAILLON (1880), on the contrary, find in the 

 axolotl : "qu'il ny a pas de canal neurenterique, que le 

 blastopore demeure toujours ouvert et qu'il devient I'anus 

 definitif". Next comes the accurate investigation of MORGAN 

 (1889, 1890) for the axolotl. He too finds that the hindmost 

 part of the blastopore passes into the anus, the anterior 

 part be'ng enclosed between the medullary folds. Since my 

 conclusions are closely akin to those of MORGAN, 1 shall 

 revert to them in detail presently. 



GOETTE (1890) similarly sees in some Urodelans (TnYon, 

 Siredonj the rear end of the blastopore pass into the anus. 



A few further observations of recent times as to tl.ie fate of 

 the blastopore may be touched on: those of De LanGE (1907, 

 1912) and ISHIKAWA (1908) concerning Megalobatrachus 

 maximus, of KUNITOMO (1911) concerning Hynobius and 

 of Smith (1912) concerning Cryptobranchus alleghaniensis. 

 All agree that the hind part of the slit-like blastopore 

 remains open as the anus, the anterior part being overgrown 

 by the medullary folds, except ISHIKAWA who considers 

 this course of events as an exception only, the anus as 

 a rule springing up as an independent formation, which is 

 denied by DE LANGE (1912). 



For Petromyzon and Dipnoans most investigators hold that 

 either the whole blastopore or its hind end passes into the anus. 



Amblystoma tigrinum —My own investigations concerning 

 the axolotl all go to confirm the conclusions reached by 

 most of my predecessors, viz: that the rear part of the 

 blastopore passes into the anus. If then 1 give a brief 

 survey of my observations, it is with the express object 

 of emphasizing some few circjmstances which v.ere not 

 noticed by former investigators and seem to me of importance 

 in giving a correct interpretation. 



The stage represented in fig. 41 a (text) and fig. 6 

 (plate III) corresponds absolutely with that of fig. 40 a and 

 fig. 1 (plate II) for Rana esculenta. Here also the medullary 

 folds begin to appear and the blastopore has contracted 

 to a short longitudinal slit. Already in fig. 6 (plate) it is 

 evident how much more the dorsal side is developed than 



