149 
greater resemblance to fig. 5, where ze medullary folds 
have coalesced, than the median one of 
At the bottom of the body the anus a broken through, 
the ventral blastopore lip as a consequence seems to have 
Suddenly vanished. The blastopore itself has been overgrown 
by the medullary folds. In the hindmost part of the medullary 
tube these folds have applied themselves so closely one to 
the other that the lumen of the tube is not continued between 
them and only a virtual neurenteric canal can be spoken of. 
From figs. 4 and 5 and from the study of whole eggs it 
appears quite evident that the medullary folds unite over 
the blastopore and that the anus breaks through a little 
distance behind it at the bottom of the small depression 
indicated in fig. 
| should like to emphasize a peculiarity which has only 
be noted by ERLANGER (1890), especially in relation to 
what we shall find in Urodelans. In the short time that 
passes between the stages of fig. |l and fig. 3 (plate II), 
the distance between blastopore and future anus diminishes 
slightly; in other words, if we take the place of the future 
anus as a fixed point, the slit-like blastopore moves a little 
backwards towards it. Thus the ventral blastopore lip 
in median sections is not only getting thinner, owing to 
the appearance of the groove between blastopore and 
anus, but also somewhat shorter. To this point we shall 
revert later. 
Different views on Urodelans. — Let us pass now to the 
Urodelans. The small extension of the ventral ectoderm 
and the strong development of the dorsal parts is here 
characteristic in the early stages of development, the 
foundation of the embryo accordingly encircling the egg 
over considerably more than 180°. The Urodelans have 
this peculiarity in common with the Dipnoans and Petromy- 
zontes of which the earlier stages of development, externally 
as well as in sections, exhibit a striking similarity to those 
of Urodelans. 
According to SCOTT and OSBORNE (1879) the blastopore 
of Triton is overgrown by the medullary folds and becomes 
the neurenteric canal. SEDGWICK (1884) in his well-known 
article on the origin of metamerism writes concerning 
Triton cristatus: “in this animal the blastopore appears not 
to close, but to persist as the anus” and his pupil ALICE 
JOHNSON (1884) verified this by sections. A neurenteric 
