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the neurenteric pore into the archenteron, and from the archenteron 
through “the neurenterie pore and the anus to the exterior. In 
ontogeny this will result in the medullary folds not closing over 
Fig. 4. Diagram of the relation between anus blastopore, and of the tail-forming 
a. at the moment of the closure of the neural folds in Anurans, 
b. Ee 5 4 = a „ Urodelans. 
c. formation of the tail. 
d. anus, p.m”. neurenteric pore; the entoderm is dotted. 
the rear end of the slit-like blastopore, but leaving an opening, the 
anus. Perhaps they will develop slightly at both sides of the rear 
part of the blastopore under the influence of the formation of the 
anus at this point, or they may not. If we imagine things very 
much enlarged and we look through the anus into the interior, 
we shall see the slit-like blastopore (neurenteric pore) in the distance, 
though its rear end, under the influence of the formation of the 
anus, will probably be widened a little. With this conception the 
facts stated by us in Urodelans so perfectly agree, that it seems 
hardly possible to doubt the correctness of this interpretation. We 
see in the axolotl the blastopore move backwards to the place 
where in Anurans the anus breaks through. We see over that place, 
that is over the rear end of the’ blastopore, the medullary folds not, 
as in Anurans, unite, but leave an opening. We have seen that we 
can pass from the medullary tube as well through the anus to the 
exterior as through the neurenteric pore into the archenteron. What 
makes things later less clear is that the medullary folds caudally 
so closely apply themselves one to another, that there is no lumen, ~ 
no medullary canal (fig. 7, plate) — just as in the frog (fig. 4) — and 
that accordingly as in the frog the neurenteric pore would become 
virtual, if the rear part did not remain open as the anus. So only 
the anterior part of the slit becomes virtual, and hence the state- 
ment of several authors concerning Urodelans, Dipnoans and Petro- 
myzontes, that the blastopore passes into the anus and a neurenteric 
canal is wanting, is to be explained. The apparent contrast between 
Anurans and Urodelans c.s. has thus found a solution. It would 
