The Nervous System of Amblystoma. " 451 



The infundibular depression in a majority of cases (id, fig. 2, 

 C, F,) begins to form where the neural groove meets the peri- 

 pheral groove, but when it appears before the formation of the 

 neural groove it lies in front of the anterior germinal depression. 

 In later stages the infundibular depression becomes a very impor- 

 tant landmark on the procephalic lobes. 



The blastopore, the transformation of which goes on more or 

 less independently^ in point of time compared with the trans- 

 formation of the anlage of the central nervous system, has now 

 in a majority of the eggs given rise to three important structures, 

 the blastogroove, the anus and the neurenteric canal. The 

 circular blastopore becomes an oval (bp, fig. 1, A, B) then nar- 

 rows into a slit (bg,fig. 1, C) and since the walls of the slit in reality 

 touch each other the slit becomes a groove, the blastogroove. 

 The length of the groove is approximately the diameter of the 

 original blastopore. In some cases it may seem to be a little 

 shorter, probably because there is a slight concrescence of the, 

 walls of the groove or slit at one or both ends. This account 

 agrees with the description given by Jordan ('95), Eycleshymer 

 ('93) and Morgan ('97) for various Amphibia. The statement 

 of these authors, however, that the anus in Salamandra is a per- 

 sisting part of the blastopore needs confirmation. It is main- 

 tained by Morgan that in the Anura the anus is a new structure 

 and in Amblystoma a careful study of this region leads to the 

 same conclusion. At this stage a posterior extension to the 

 blastogroove has appeared carrying the slit backward until it 

 touches the groove which in earlier stages bounds the blasto- 

 poric lip (bg, fig. 2, B, fig. 2, B, a). This backward extension 

 of the blastogroove is the anus. In other words the anus in 

 Amblystoma forms directly behind the blastogroove and in 

 connection with it, so that in appearance it is the posterior end 

 of the groove, there being no distinct boundary between the two. 

 This forms a condition between that of the frog, where the anus 

 develops separate from the blastogroove, and that of the newt, 

 where if Morgan's account is correct the anus is a persisting 

 part of the blastopore. At the anterior end of the blastogroove 

 there remains a small pore, the neurenteric canal (nee, fig. 2, B). 



