135 
more than 180°. The place where the dorsal blastopore 
lip first appears is in all three cases nearly the same, 
being situated a little beneath the equator of the egg. The same 
holds good for the place where the crescent-shaped blastopore 
border closes to a ring, i. e. where the ventral lip first 
appears. In all three cases this is close to the vegetative pole. 
In Rana esculenta, however, we see the ventral lip mov- 
ing forward more actively than in Rana fusca, which 
causes the blastopore to close at a place situated more to 
the dorsal side than in Rana fusca. 1 must rectify here 
a statement made with some reserve in a former paper 
(1916). 1 gave a figure (fig. 8, p. 8) in which the border 
of the blastopore, at the moment it has just closed to a 
ring, was provisionnally indicated with a dotted line, since 
T had not observed it in the egg figured there but had 
transferred it into this figure from other eggs. Afterwards, 
however, repeating my experiments I could state that the 
latter eggs were such that had been developing abnor- 
mally and showed a tendency to the “spina bifida” phe- 
nomenon. In normal eggs the blastopore has never so 
large a diameter which seems to be caused by a bulging 
out of the yolk-plug and a temporary forward instead of 
backward movement of the dorsal blastopore lip, as men- 
tioned above. Thus this dotted line must be removed from the 
figure. Further experiments have also given me the impres- 
sion that the movement of the ventral lip has been shown 
a little too large in this figure and that in reality it does 
not move faster than the dorsal lip. Also the dorsal movement 
of the whole white area, to which 1 thought it inevitable 
to conclude from the observed facts, was not confirmed by 
the observation of eggs marked at both the vegetative and 
the animal pole. As far as l could state both marks remained 
exactly opposite each other during the cleavage and the 
gastrulation, just as in Rana fusca. 
Thus the difference between Rana fusca and Rana 
esculenta appears to be much less than 1 first concluded 
from experiments on eggs, part of which afterwards proved 
to develop abnormally. In Rana esculenta the ventral lip 
moves only a little more actively than in Rana fusca, and 
also in longitudinal sections the ventral lip appears to be 
a little more strongly developed than in the latter form. 
The reverse case is found in Amblystoma. Here the 
dorsal blastopore lip, after its first appearance a little 
