Vol. 8, 1922 
BIOLOGY: A. H. CLARK 
223 
this internal colony has reached its maximum in the cephalochordates and 
the vertebrates. 
The correctness of the interpretation of the segmented animals as pri- 
marily consolidated colonies is indicated by the retention in all the in- 
cluded groups — the cestodes, annelids, crustaceans, echinoderms and 
insects — of some form of asexual reproduction, budding, budding and fis- 
sion, fragmentation, polyembryony or parthenogenesis which, though 
greatly reduced in the more specialized types, especially in the insects, 
may be traced back to the budding and budding and fission characteristic 
of the coelenterate- colonies. 
The correctness of the interpretation of the unsegmented animals (except 
those with gill apertures) as ingrown colonies is indicated in all the in- 
cluded groups — the priapulids, sipunculids, molluscs, nemerteans, 
phoronids, brachiopods, and chaetognaths — by the entire absence of asex- 
ual reproduction of any kind, this having been rendered impossible through 
the transference of the colonial development to the interior. 
For the sake of clearness no mention has been made of the fact that 
the annelids, crustaceans, echinoderms and insects, belonging to the seg- 
mented series, also possess coelomic structures and are to a certain extent 
therefore doubly colonial. In the annelids the two structural remnants of 
the primitive colony are about equally balanced. In the crustaceans and 
insects the coelomic structures have almost disappeared in favor of the 
development of the segmentation. In the echinoderms the body is reduced 
to five half segments while the coelome is highly developed. 
With the segmentation and the development of the coelome considered 
as derived from a fundamentally colonial habit there is no fundamental 
body form nor structure in the bilateral animals which cannot be traced 
back to an origin in the colonial coelenterates. The cestodes and the 
trematodes represent the transition forms in which we see the colonial 
habit and the radial symmetry of the coelenterate type breaking down and 
passing into the solitary habit and bilateral symmetry of the "higher" 
animals in which little or no traces either of the primitive radial sym- 
metry or of asexual reproduction remain. 
These numerous forms, the annelids, crustaceans, echinoderms and in- 
sects on the one hand and the priapulids, sipunculids, molluscs, nemerteans, 
phoronids, brachiopods, chaetognaths, enteropneusts and vertebrates on 
the other are so inextricably entangled in a network of lines connecting 
each more or less definitely or vaguely with all the others and even crossing 
the gap between the two groups that it is quite beside the mark to speak 
of evolution in connection with them. Each phylum represents a sort of 
crystallization center about which a greater or lesser number of forms all 
showing but little deviation from a fixed type are closely grouped within 
a definite but broad and general structural complex. 
