1265 
‘part remains open as the internal opening of the anus. The result 
is really that the hindwall of the hindmost part of the medullary 
tube is perforated by the anus, which in Anurans arises directly 
behind it, and this is caused by the circumstance that the neurenterie 
pore, the former blastopore, in Urodelans has travelled back so far, 
that its rear end has reached the place where in Anurans the anus 
breaks through. This is at the same time the solution of the apparent 
contradiction between Anurans and Urodelans in this respect. 
The interpretation which until now has been pretty generally 
adopted is that of ScHanz (1887), Morean (1890), ErraNGER (1890) and 
ROBINSON and AssHeTON (1891), who contend that the place where the 
anus in Anurans breaks through really represents the rear end of the 
original wide blastopore, which has narrowed down by concrescence 
of the lateral borders not only at the anterior end, as postulated by 
His’s conerescence theory, but also at the posterior end. The longi- 
tudinal groove between the blastopore and the anal depression in 
fig. 1 seemed to be an indication of a raphe. Thus the anus in 
Amphibia would be closed only temporarily and would not arise as 
an independent formation. In this way ERLANGER assumed concrescence 
at the dorsal as well as at the ventral blastopore border, ROBINSON 
and AssHETON only at the ventral border. The line of concrescence 
in both cases is compared to a primitive streak, which, as ROBINSON 
and AssHETON in accordance with BALFOUR’s views on this point 
remark, can be expected only behind the blastopore: wrongly enough 
the adherents of the doctrine of concrescence call primitive streak 
the concrescence-seam assumed by them in front of the blastopore. 
To me it seems that one ought to add that a primitive streak is to 
be expected only in yolk-laden eggs with a germinal dise or in eggs 
that are to be derived from yolk-laden ones. 
I will not absolutely deny that concrescence ever plays a part in 
vertebrate gastrulation, especially in yolk-laden eggs. But that its 
rôle is a much more subordinate one than the well-known doctrine 
of His assumes, seems to me beyond doubt. Even by students of the 
development of teleosteans, which seemed to afford the most acceptable 
confirmation of it, His’ doctrine is rejected, as for example by SumMEr 
(1904). For amphibians the pricking experiments described in both 
my former communications have shown that there cannot be any 
question about the whole dorsal side of the embryonic rudiment 
arising by concrescence of the blastoporic lips. 
It is quite true that in the amphibian egg a fine median line is 
often seen running from the blastopore forward, which strongly 
suggests a concrescence-raphe. Only, as Ropinson and AssHETON 
