62 James Francis ABBort, 
C. General considerations. 
Struck by the similarity in habits and form between Coeloplana 
and the Polyclads, Lane, 1884, attempted to utilize KowALEvSsKY's 
discovery as the basis of a possible origin of the latter from the 
Ctenophores through Coeloplana. While it is not probable that any 
morphologist accepts Lane’s hypothesis nowadays it may be noted 
that in addition to the erroneous homologizing of the axes of the 
body in the Ctenophora, discussed by Wırney, Lane was no doubt 
led astray by the reviewer in the Zoologischer Anzeiger (vide ante) 
so that he homologized the excretory tubes leading upward from 
the infundibulum (a structure characteristic of Ctenophores) with 
the anterior branch of the gastric system of the Polyelads. 
Wirtey, 1896, with the more exact knowledge obtained from 
his own and Korotnerr’s studies on Ctenoplana avoided this mistake 
but contended that Ctenoplana is a primitive form, rather warmly 
denying any imputation of its being degenerate, as a “groundless 
assumption”. He places his Cfenoplana in an order, the Archiplanoidea, 
from which he derives the Ctenophora on the one hand and the 
Platyhelminthes on the other. It will be seen that the value of this 
arrangement depends wholly upon whether Ctenoplana is to be con- 
sidered a primitive form or not and the arguments WILLEY advances 
in support of his assertion are not wholly conclusive. It must be 
conceded that Ctenoplana stands midway between Coeloplana and the 
Cydippid Ctenophores, in regard to either its primitiveness or its 
“degeneracy”. Coeloplana is wholly without costae: Ctenoplana is 
scantily provided with costae. Coeloplana has practically given up, 
or, from Wittey’s point of view, never acquired the pelagic habit 
while Ctenoplana both swims and crawls. 
If Ctenoplana is primitive, then Coeloplana is certainly so to a 
greater degree, and if we find in Coeloplana structures that can 
only be explained as the result of the reduction, through disuse, of 
structures characteristic of pelagic Ctenophores and’ associated with 
their pelagic habit, then the presumption is clear that it cannot be 
a primitive form in WıLuey’s sense and that the Ctenophora cannot 
be derived from it. In fact the weight of the morphological evidence 
bears out the conclusion that Coeloplana is a very highly specialized 
Ctenophore derived from the Cydippida. 
Among the structures found in Coeloplana which are characteristic 
of the pelagic Ctenophores may be mentioned 1) the median funnel 
