192 
Vertebrates to Chordonia was a necessary consequence of 
KOWALEWSKY’s (1866) embryological work. GROBBEN now 
designated the Zygoneura as Protostomia, and opposes them: 
to both the other groups as Deuterostomia, since in the 
former the blastopore directly passes into the ingestion- 
opening, whereas in Deuterostomia it passes into the 
egestion-opening, the anus, or at least exhibits certain 
relations to the latter and none to the mouth, which is 
formed as a secendary perforation quite independent from 
the blastopore. The first to attribute such a primary 
importance to the fate of the blastopore has been GOETTE 
(1884), who distinguished the hypogastric from the pleuro- 
gastric Bilateria. In the former, to which Annelids, Nemertines, 
Nematodes etc. belong, the blastopore passes into the mouth, 
in the latter, comprising Vertebrates, Echinoderms and 
probably also Enteropneusts, into the anus. 
hus the place assigned to the Chordates in this system is 
in agreement with ‘he attempts of BATESON (1886) and his 
followers to found a relationship between Chordates and 
Enteropneusts and by means of the latter again with. 
Echinoderms (cf. GARSTANG, 1894), to which the Enterop- 
neusts are undoubtedly related. I will not go here into a 
criticism of BATESON's theory. Others, more competent 
than 1, as e.g. SPENGEL (1893, p. 721), have done this 
already and have shown how unconvincing are the homo- 
logies proposed by BATESON. Indeed, if we ask ourselves 
with which group the Chordates show closer affinity, 
whether with the Annelids, a trunk to which more than 
one branch showing tendency to higher development — like 
Arthropods and Molluscs—is related, or with the dull 
Echinoderms with their lack of intellectual and other develop- 
ment, the answer can be hardly doubtful. 
My theory. — The theory on the origin of Vertebrates, 
which 1 published some years ago (1913), can be ranked 
among those theories which in different ways try to find 
a solution of the difficulties connected with the derivation 
of Vertebrates from Annelids; difficulties which have resis- 
ted for so long all attempts to overcome them, that the 
case seemed to appear almost hopeless. 1 must emphasize, 
however, that, unlike most of the authors cited in the 
beginning of the next chapter, it was not in the least 
my intention to make an attempt to render DOHRN's and 
SEMPER's theory acceptable, nor to look for a solution of the 
