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less developed and leave an opening, the anus. Comparing 
my description with that of former investigators it will be 
noted that, keeping strictly to the facts, t yet present them 
in a somewhat different way: | do not let the medullary 
folds finish halfway along the length of the blastopore slit 
but only in closing leave an opening over the rear end of 
the blastopore, the anus. Accordingly one can, retracing 
the medullary canal, not only pass through the neurenteric 
canal into the archenteron but also through the anus to 
the outside, this being nowhere prevented by a coalescence 
ge ed 
Fig. 42. hee gate sections through the blastopore of an egg 
mbtystoma punctatum, where the medullary folds 
just close over it, after MORGAN, 
a in front of the blastopore, b and € through anterior 
half, d and e through rear end (anus 
of the two medullary folds across the middle of the blasto- 
pore, as several investigators are inclined to assume. 
in a longitudinal section (fig. 8, plate Ill) the 
blastopore (bl.=p. neur.) and the anus (a) are easily 
distinghuishable from one another. The blastopore becomes 
the neurenteric canal or, perhaps better, the neurenteric 
pore (porus neurentericus), as 1 prefer to call it henceforth. 
Entering the anus, one can pass through the neurenteric 
pore into the archenteron. The arterior part of the neuren- 
teric pore, however, becomes — and is already in fig. 8 — 
virtual, the medullary folds applying themselves behind so 
closely to one another that the lumen of the medullary 
