No. 2.] THE DEVELOPMENT OF THE NEWT. 335 



The anus in the Anura is apparently, in some forms at least, 

 a new formation in the region of the primitive blastopore. 

 Although my own observations have thus far been exclusively 

 upon the newt, and my belief has consequently the weight 

 only of an obiter dictum, I think the careful observations of 

 Schanz ('87), Erlanger {'9i), and Robinson and Assheton ('9l), 

 are deserving of acceptance. Even if we admit the possibility 

 that the fate of the blastopore is different in other members of 

 the same group, I see no way of escape from the facts adduced 

 by these authors in the specific instances which they consider. 

 It is possible, nay probable, that variations even among indi- 

 viduals of the same species may account for the discordant 

 results of other investigators. Viewed in the light of Erlanger's 

 suggestion ('89, p. 251), that the Anuran anus should be re- 

 garded as a secondary formation, I see no reason why we 

 should not expect occasional and perhaps frequent reversion to 

 the more primitive condition. I may here suggest that the 

 interesting observations of Ziegler ('92) on the living Qg^ of 

 Rana may perhaps be referable to some such explanation. 

 Ziegler's observations, moreover, although highly interesting 

 and important, afford no conclusive proof of the actual per- 

 sistence of a portion of the blastopore opening. There is 

 nothing in his figures that proves that the depression pictured 

 communicates at all stages with the archenteron. That, I take 

 it, could be demonstrated only by sections, though it is a sup- 

 position which the surface indications render plausible. 



In the case of the Urodela there seems to be greater una- 

 nimity of opinion. The work of Miss Johnson ('84), Schanz 

 ('87) and Morgan ('89) have practically established the fact that 

 the Urodelan anus is a remnant of the blastopore which has 

 remained open from the first. I shall show presently that my 

 own observations on DiemyctyliLS support this view. 



This main fact, however, admits of many variations of opinion 

 as to essential details. What portion of the blastopore is it 

 that persists as the anus } What are the relations of the so- 

 called neuropore to the blastopore and to the anus '^. How is 

 the primitive streak related to the blastopore .'' What is 

 the method of closure of the blastopore .-' It is clear that 



