914 
more intelligible when we see that during gastrulation the whole 
entoderm area performs a wandering forward. The assumption 
that the situation of the blastoporic rim at this stage as dotted 
in fig. 8, is right, is also favoured by the fact, that the line 1—1 
thus runs parallel to the boundary between the darker and the 
lighter area of the egg, as indicated in fig. 3. This becomes evident, 
if we hold the figures 3 and 8 up to the light one upon the other, 
in such a way that the points a coincide. Just as in Rana fusca 
we also find in Rana esculenta that this line of demarcation in 
the different stages always runs parallel to the blastoporic border, 
approaching it gradually, until at last it reaches it. 
el 
Fig. 6. The same egg, from the side, May 8, 9.15 p.m. 
Now in holding up to the light one upon the other the figs. 4, 5 
and 6, in such a way that the marks « each time coincide, it may 
be stated further that the distance of the points a and 5, just as in 
Rana fusca, increases only very slightly, and moreover the way 
in which the blastopore contracts may be studied in detail. This 
same method was adopted again in composing the summary figure 8. 
While in Rana fusca the ventral blastopore border, which there 
appears approximately diametrically opposite the animal pole, does 
not make any forward movement, in Rana temporaria it not only 
does so, but the ventral border even progresses still more rapidly 
than the dorsal one! 
Although some time after drawing fig. 6, I found the marks 
