292 Proceedings of Royal Society of Edinburgh. [sess. 
In the adult the body-form, as in the Brachiopoda , has under- 
gone great modification, and differs little from fig. 4 in general 
features, whilst fig. 6 shows the inter-relationship of the archicceles. 
As in Brachiopoda , the protocoele communicates secondarily with 
the mesocoeles, and the metacoelic pores are nephridial and gona- 
ducal. 
The simple nervous system, in continuity with the ectoderm, 
with a protomeric ganglion and a post-oral nerve-ring, and the 
arrangement of the vascular system, are all in close agreement 
with the archi-coelomate type. The true zoological position of this 
group will he discussed in a paper upon its anatomy now in the 
course of completion, so that its claims to be considered one of the 
Ar chi-coelomata can alone be dealt with. 
The actual fate of the five archicoeles in Adinotroclia has not 
been fully followed, hut there is some ground for believing that 
the epistome-cavity is derived from the protocoele, the ‘body- 
cavity ’ in front of the septum from the mesocoeles, and that 
behind it from the metacceles (see fig. 4). 
Polyzoa. 
This very heterogeneous group may yet prove to contain several 
distinct phyla, and is already held by many to be di-phyletic, the 
Ectoprocta and Entoproda being regarded as convergent. 
In Korschelt and Heider’s work, and more recently in Parker 
and Haswell’s text-book, the Polyzoa ( Edoproda ), Brachiopoda , 
and Phoronis are placed together under the old title Molluscoida 
(cf. figs. 4 and 6). 
Their features in common are most probably to be derived as 
follows : — Firstly, there is an underlying basis of resemblance in 
fundamental characters, such as archimeric segmentation * and other 
characters, which have been given here as archi-coelomate characters, 
which these groups possess, in virtue of a common descent, from an 
archi-coelomate ancestry, and to this extent the groups are genet- 
ically connected. Secondly, there is a series of more superficial 
morphological resemblances, which are to be traced directly to the 
influence of the sedentary habit which each group has indepen- 
* Cori. Zeits. f. w. Zool., Bd. 51. 
