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with a germinal disc, or in eggs that are to be derived 
from yolk-laden ones, such as those of Mammals. 
As stated earlier, 1 shall not absolutely deny that concresc- 
ence ever plays a part in Vertebrate gastrulation, particularly 
in yolk-laden eggs. It seems to me beyond doubt, however, 
that its rôle is a much more subordinate one than the well- 
known doctrine of HIS assumes. For Amphibians the pricking 
experiments described above have shown that there can 
be no question of the whole dorsal side of the embryonic 
rudiment arising by concrescence of the blastoporic lips. 
or concrescence at the hind border of the blastopore, 
as assumed by ROBINSON and ASSHETON, still less evidence 
can be adduced. The groove between the slit-like blastopore 
and the anal pit does not become gradually longer, as 
might be expected in this case, the anal pit moving away 
from the ventral border of the blastopore, but on the contrary 
it only gradually becomes more distinct ard at the same 
time shorter, the blastopore approaching the anal pit. 
Evidently it is not to be considered as a concrescence- 
seam, perhaps it may be compared to the groove 
joining the two impressions made by two fingers pressed 
near one another into a soft cushion. When ROBINSON 
and ASSHETON (1891, p. 475) compare it with the primitive 
streak eg. of a bird, they encounter at once the difficulty 
that in the latter it is formed from in front backwards, in the 
frog egg, according to their assumption, from behind forwards. 
Three possibilities may be distinguished concerning the 
relation between blastopore and anus in Vertebrates: 
there is a primary relation 
2. there is no relation 
3. there is a secondary relation. 
Primary relation between anus and blastopore. — The first 
supposition mentioned above is now the one most widely 
accepted. Even where in Anurans 2 seems to prevail, yet 
it is assumed that this is to be traced back to 1, since 
what is found in Urodelans may be supposed to be valid 
for Anurans also. Thus MAURER (1906) in HERTWIG's 
Handbuch tries to trace back all the results for Chordates 
to 1, though the evidence adduced can not always be called 
convincing. Even in Amphioxus no relation between the 
anus and the blastopore has as yet been established. 
The possibility of 1 is in no way precluded by my theory 
which derives the Chordates, in opposition to GROBBEN, 
