1264 
itself constituting the neurenteric canal. Figs. 3d and e are still 
further back, the medullary folds are less developed, and leave an 
Ss 
ZA 
Fig. 3. Transverse sections through the blastopore of: an egg of 
Amblystoma punctatum, where the medullary folds just close over it, 
after Morgan (1890). 
a in front of the blastopore, 0 and c through anterior half, 
d and e through rear end (anus). 
opening, the anus. Comparing my description with that of former 
investigators it will be noted that, keeping strictly to the facts, I 
yet present them in a somewhat different way: I do not let the 
medullary folds finish halfway 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 of the two medullary folds across the middle of 
the blastopore, as many investigators are inclined to assume. 
Now in a longitudinal section (fig. 7, plate) the blastopore (bl. = p. 
neur.) and the anus (a) are easily distinguishable from one another. The 
blastopore becomes the neurenteric canal or, perhaps better, the 
neurenteric pore (porus neurentericus), as I prefer to call it hence- 
forward. Entering the anus, one can pass through the neurenteric 
pore into the archenteron. The anterior part of the neurenteric pore 
however becomes — and is already in fig. 7 — virtual, the medul- 
lary folds applying themselves behind so closely to one another, that 
the lumen of the medullary canal is not continued any further 
between them, as Morean has already remarked. Hence the opinion 
of many investigators that the medullary folds do not reach to the 
blastopore and that there is no neurenteric canal. The hindmost 
