909 
fact does not represent the same egg, a circumstance, which having 
regard to the great uniformity of the eggs in this respect, does not 
imply any difficulty. From this however one must in no way 
conclude, that the cells containing the pigment perform such a 
wandering downward themselves. The behaviour of the marks at 
b, c, and d in the different eggs tells us otherwise: their distance 
from the animal pole just as in Rana fusca increases only very 
slightly. Besides, former investigators have already pointed to the 
fact that during development the formation of new pigment goes 
on, especially at places of great cell-activity. 
a 
Fig. 4. The same egg, from the side, May 8,6.30a.m. 
Unfortunately the next figure of the egg, was drawn much later 
(fig. 4), when the blastopore had already been contracting for some 
time. Other eggs however teach us, that, when the border of the 
blastopore has just closed at the rear side to a ring, this ring is 
much wider than in Rana fusca. While in the latter species the 
longitudinal diameter of the blastopore is about 60°, in the former 
it amounts to no less than 120°, about twice as much. So the exact 
situation of tbe anterior and posterior border in this stage in regard 
to the points a and 5 could not be made out and in the fig. 8, 
which is a composition of the other figures, I have accordingly 
indicated the border of the blastopore with a dotted line, as it 
will probably run. I have indicated the anterior border as lying a 
little in front of the place where the first trace of the invagination 
became visible, which accordingly would point to a primary backward 
