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egg and to this end begin with the egg of Rana fusca. At once it 
appears that the first of the three above-mentioned processes, the 
wandering of the entoderm area to the ventral, ce. q. to the dorsal 
side, is here performed very precociously, immediately after fertili- 
zation, and consequently is already finished in the unsegmented, 
fertilized egg. At least we find, as is shown by fig. 1 of my former 
communication, that the white area here does not lie at all diame- 
trically opposite the animal pole, but much more to the future 
dorsal side. The boundary between the ecto- and entoderm areas 
probably runs parallel to the demarcation of the darker and lighter 
areas of the egg, as may be also concluded from the place, where 
afterwards the dorsal and ventral borders of the blastopore appear 
(fig. 2, ibid.). Evidently we have to deal here with a case of pre- 
cocious segregation, though it concerns here more a wandering than 
a segregation. 
The second process mentioned above, the rostrad-excentrical closure 
of the blastopore, we do not find in Rana fusca; on the contrary, 
the closure proceeds caudad-excentrically. As mentioned already in 
my former communication and elsewhere, I see in this caudad- 
excentrical closure a result of the interference of the contraction 
of the blastoporic border with a backward movement of the blas- 
topore, following directly from my theory on the homology of 
stomodaeum and epichordal neural tube in annelids and vertebrates. 
As a result of the strong elongation which we must assume that 
the stomodaeum of annelids undergoes to be transformed into 
the medullary tube of vertebrates (ef. the scheme in my article 
in. Anat. Anz. Bd. 44, p. 493), the entrance to the stomach 
(Schlundpforte, HarscneK), into which the blastopore passes, must 
perform a wandering over nearly the whole length of the body 
to become the neurenteric canal (also resulting from the blastopore). 
This backward wandering now in chordates is performed in anti- 
cipation of the formation of a tube, already during the contraction 
of the blastopore border. By this process the final, narrowed blastopore 
is carried back to the place where it was originally found in 
Protaxonia, viz. diametrically opposite the animal pole. Whether this 
caudad-excentrical closure of the blastopore is performed by concres- 
cence or not, is here of no importance; as stated earlier, 1 do not 
believe that concrescence, at least in amphibians, occurs to any 
considerable extent. The medullary plate, of which the foundation 
in stage 10e, just as the foundation of the stomodaeum in fig. 105, 
surrounds as a crescent the anterior border of the blastopore — a 
conclusion reached for Amphioxus also, e.g. by KorscHELT and 
