1262 
and Isurkawa (1908) concerning Meyalobatrachus maximus, of Kuxrromo 
(1911) concerning Hynobius, and of Smrrm (1912) concerning Crypto- 
branchus alleghaniensis. All agree in this that the hind part of the slit- 
like blastopore remains open as the anus, the anterior part being 
overgrown by the medullary folds, except IsHikawa, who thinks this 
course of events to occur only exceptionally, the anus as a rule 
Springing up as an independent formation, which is denied by 
DE LANGE (1912). 
For Petromyzon and Dipnoans most investigators hold that either 
the whole blastopore or its hind end passes into the anus. 
My own investigations concerning the axolotl all go to confirm 
the conclusions already reached by most of my predecessors, viz. 
that the rear part of the blastopore passes into the anus. If then I 
give a brief survey of my observations, it is with the express object 
of emphasizing some few circumstances which were not noticed by 
former investigators and seem to me of importance in giving a 
right interpretation. | 
2a 2b 2c 2d 
Fig. 2. Three eggs of Amblystoma tigrinum during the closure of the 
medullary folds. 
a. seen from behind, b. dorsally, c. (the same as b) and d. ventrally. 
a. anus, bl. blastopore, h.p. cerebral plate, k. head. 
The stage represented in fig. 2a (text) and fig. 5 (plate) corresponds 
absolutely with that of fig. 1a and fig. 1 (plate) for Rana esculenta. 
Here too the medullary folds begin to appear and the blastopore has 
contracted to a short longitudinal slit. Already in fig. 5 it is evident, 
how much more the dorsal side is developed than the ventral side, 
the distance from the animal pole (which according to EycLESHYMER, 
1895, here too is to be found back just in front of the transverse 
