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communication, on the wandering of the dorsal blastopore border. 
Rovx’s opinion was, that only the dorsal rim wanders over the 
yolk, which for Rana fusca proves to be right, though not 180°. 
SCHULTZE on the contrary declared all movement of the dorsal 
border to be illusory and to be explained by a rotation of the egg. 
Actively, according to him, the entoderm wanders forward under the 
dorsal border, and it appears by our present results that ScHuurze’s 
view, at least as far as Rana esculenta is concerned, is not quite 
erroneous either. 
Now apparently we have in this wandering of the entoderm area 
during gastrulation in Rana esculenta the same dorsally directed 
movement before us, which in Rana fusca is performed immediately 
after fertilization, and which there causes in the eight-celled stage 
the demarcation line between the darker and lighter area of the egg 
surface to make a so much greater angle to the egg equator than 
in Rana esculenta, while for the blastopore border, just after it has 
closed to a ring, the same holds. All this is shown at once by a 
comparison of fig. 1 and 8 of the present paper with fig. 1 and 2 
of the former. 
Before looking now for the explanation of the phenomenon, a 
short discussion must precede of the views, to which my theory of 
the origin of vertebrates leads concerning the gastrulation of verte- 
brates, in the first place of anamnia. In studying this theory many 
a one will have wondered how from two in Protaxonia (HATSCHEK) 
diametrically opposite areas as the apical plate (round the animal 
pole) and the stomodaeum (round the blastopore) in craniote verte- 
brates an organ could arise, which so much gives the impression 
of a unity, as the cerebral and the medullary plate. A considerable 
displacement at any rate must have occurred, to bring together 
these two parts. 
This approach we now see performed before our eyes in the 
ontogeny of annelids. While the entoderm, which remains after the 
production of the three quartets of ectomeres, originally lies diame- 
trically opposite to the animal pole, we find the mouth, which is 
directly to be traced back to the blastopore, in the trochophora lying 
just under the prototroch, which forms the border of the apical plate. 
As discussed in my article on the development of Scoloplos armiger, 
the displacement is to be ascribed to three factors. 
In the first place we observe a wandering of the whole entoderm 
area to the ventral side (Fig. 104), a result of the active multiplication 
and extension of the ectoderm cells at the rear side, i.e. mainly 
the d-quadrant of the egg, whereas the cells of the anterior side, 
