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from Protostomia, as long as the possibility of a relation 
between the anus and the blastopore in the latter group 
exists. This might be expected from SEDGWICK’s well-known 
theory (1884) which derives the mouth and the anus of 
Bilateria from the anterior and the posterior extremity of 
a slit-like Actinian mouth of which the borders coalesce 
in the middle. It ought then to be possible to trace the 
concrescence-seam joining mouth and anus, which accot- 
ding to this theory should run over the ventral side of Annelids, 
in Vertebrates also in the groove between anus and blasto- 
pore, that is in the so-called “Afterrinne,” the “primitive 
streak’ of ROBINSON and ASSHETON (see above) — not in the 
hypothetical concrescence-raphe in front of the blas:opore, the 
“primitive streak” of the theory of concrescence, as LAMEERE 
(1891) and HUBRECHT (1905) assume in their application 
of SEDGWICK’s theory to Vertebrates. Thus the presence 
of a primary relation between the anus and the blasto- 
pore in Vertebrates would in no way compel us to derive 
them with GROBBEN (1908) from the Deuterostomia, as long 
as the possibility of a similar relation in Protostomia exists. 
However, the theory of SEDGWICK finds in the develop- 
ment of Protostomia just as little support as Ì hope to 
show is the case in Tritostomia (Vertebrates). A process 
of such fundamental phylogenetic significance as assumed 
by SEDGWICK's theory might be expected to have left more 
distinct traces in the ontogenetic development than are 
demonstrated by the most careful research of recent inves- 
tigators. Again and again we see the anus arise as a new 
formation, by perforation. In Annelids, where primarily 
we might expect to find evidence of a common origin of 
mouth and anus, a direct transformation of the rear end of 
the blastopore into the anus has never been established. 
Even in the primitive Polygordius, where as a matter of 
fact the blastopore is divided into two halves by a median 
constriction (WOLTERECK, 1904), the posterior openings 
nevertheless closes and the anus is formed by perforation 
behind the two teloblasts which lie at the rear end of the 
blastopore. To me, as stated before, the most probable 
conception of the origin of the anus seems to be that in 
a larva of the protrochula-type (MüLLER's larva of a Poly- 
clad, pilidium of Nemertines) the entodermal pouch, which 
is already turned in a backward direction, has com€ iN 
contact with the ventral body wall and has broken through by 
