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over the blastopore and that somewhat behind it at the bottom of 
the little depression indicated in fig. 1c (text) the anus breaks through. 
I should like to emphasize a peculiarity which has only been 
pointed out by ERLANGER (1890), especially in relation to what we shall 
find in Urodelans. In the short time that passes between the stages 
of fig. 1 and fig. 3, the distance between blastopore and future anus 
diminishes a little; 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. So 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 will revert later. 
Let us pass now to the Urodelans. Characteristic in the early 
stages of development is here the little extension of the ventral ecto- 
derm and the strong development of the dorsal parts, the foundation 
of the embryo accordingly encircling the egg over considerably more 
than 180°. This peculiarity the Urodelans have in common with the 
Dipnoans and Petromyzontes, of which the earliest stages of devel- 
opment, externally as well as in sections, exhibit a striking similarity 
to those of Urodelans. 
According to Scorr and OsBorNr (1879) the blastopore of Triton 
is overgrown by the meduilary folds and becomes the neurenteric 
canal. Sepa@wick (1884) in his well-known article on the origin of 
metamerism writes concerning Zriton cristatus: “in this animal the 
blastopore appears not to close, but to persist as the anus” and his 
pupil Arice Jonnson (1884) verified this by sections. A neurenteric 
canal, as described by Scorr and OsBoRNE, was never observed by 
her. Scuanz (1887) in Triton punctatus comes to the conclusion that 
the blastopore is constricted in the middle, the anterior opening 
becoming the neurenteric canal, the posterior opening the anus. 
Hovussay and BararLLoN (1880) on the contrary find in the axolotl: 
“qu il n’y pas de canal neurentérique, que le blastopore demeure 
toujours ouvert et qu'il devient Vanus définitif.” Next comes the 
accurate investigation of Morean (1889, 1890) for the axolotl. He 
too finds that the hindmost part of the blastopore passes into the 
anus, the anterior part being overgrown by the medullary folds. 
Since my conclusions are closely akin to those of Morcan, 1 will 
revert to them in detail presently. 
Gorrre (1890) similarly sees in some Anurans (F'riton, Stredon) 
the rear end of the blastopore pass into the anus. 
A few further observations of recent times as to the fate of the 
blastopore may be touched on, thus those of pr Lance (1907, 1912) 
