913 
For the sake of completeness in fig. 8 the position of the marks 
c and d, from another series, has also been indieated. As already 
Fig. 8. Combination of figs. 3—7 and others, from which 
the situation of c and d and the extension of the 
blastopore in phase 1 are borrowed. lebl= first 
indication of the blastopore (fig. 2 and 3). 
observed before, the mutual distance of the marks a, b, c, and d, 
just as in Rana fusca, changes but little during cleavage and gastru- 
lation. Yet it could be stated that the distance a—c increases 
somewhat. 
Very conflicting views have up to the present day been held as to the 
gastrulation of vertebrates. To many an adherent of one of these 
views the result of the recorded pricking experiments will be some- 
what surprising. Who, after studying fig. 8, could maintain any 
longer that the foundation of the dorsal parts of the embryo originally 
lies as a ring round the border of the blastopore and is formed 
from it by conerescence? By far the greater part of the embryo is 
formed in front of the place, where the dorsal blastoporic rim first 
appears, and the contraction of the blastopore proceeds nearly con- 
centrically. An explanation of the facts mentioned seems to me to 
be afforded by the views concerning the gastrulation, which follow 
from my theory on the derivation of vertebrates from annelids. 
To this end let us first consider once more the movement of the 
ventral blastoporic border. Have we to deal here with a similar over- 
growth of the yolk as at the dorsal lip? In that case we ought to 
