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by Durnam (1886), but secondarily, according: to the latter, a neuren- 
teric canal is formed, independent of the blastopore. Kuprrrr (1887), 
dealing with the same subject, comes to the conclusion that the 
blastopore remains open as the anus; so, too, PrrEenyr (1888). 
ScHaNz (1887) also operated on Rana temporaria, together with 
Triton. In Rana he concludes that the medullary folds rather close 
over the blastopore, that there is indeed a neurenteric canal, though 
the lumen is not evident, and that the anus arises by perforation 
at the bottom of a little groove behind it. As regards, the facts 
SIDEBOTHAM (1888) quite agrees with him. According to him BaLrour’s 
description is the right one, he too sees in sections the ‘diverticulum 
from the hind end of the mesenteron, dipping down towards a 
distinct pit in the epiblast below the blastopore and quite separate 
from it”. Eventually perforation ensues. Similarly by Morean (1890) 
in Rana halecina and Bufo lentiginosus the anus is seen to arise 
at the bottom of a little groove in the ectoderm behind the blastopore. 
Gorrrr (1890) after a renewed investigation on Bombinator igneus 
and some other Anurans reaches the conclusion that the anterior 
half of the shit-like blastopore is transformed into the neurenteric 
canal, the posterior half into the anus. Yet in Pelobates he claims 
that this posterior half first closes and that the anus is formed 
only later. | 
As is apparent from the foregoing, during this period nearly every 
year brought forth a new investigation on this subject. In 1890 
that of ERLANGER on Rana esculenta appeared; in 1891 that of 
RoBINsoN and AssHeToN on Lana temporaria; in the same year 
a small treatise by ERLANGER in reply to some observations made 
by the two English critics on his work. All agree however that in 
both cases the anus arises by perforation. 
In later years the fate of the blastopore is alluded to only ina 
few investigations, e.g. by Brrs (1905), who for Xenopus laevis, 
and by Sremann (1907), who for Alytes obstetricans shows that the 
blastopore is not enclosed by the medullary folds and passes directly 
into the anus, there being accordingly no neurenteric canal. 
Most of the investigators who have paid special attention to the 
question thus come to the conclusion ( which after my own exami- 
nation of Rana esculenta I can support without reservation) that 
the anus arises by perforation a little distance behind the blastopore, 
which is transformed into the neurenteric canal. A short description 
may be given here in addition to the figures for Rana esculenta. 
After the yolk-plug has disappeared from the surface the blastopore 
presents itself as a short longitudinal split (texttig. 1a). A median 
