306 Proceedings of Royal Society of Edinburgh. [sess. 
applies to some at least of the Sipunculids, though more know- 
ledge is required with regard to the origin and arrangement of the 
coelome in these types.* 
These groups are all placed with those which have been above 
referred to as one group, Vermidea , quite recently by Professor 
Delage,f and it would he superfluous to add here his arguments for 
this grouping. For the present, I would not weaken the argument 
by definitely claiming to be included in the Ar chi-coelomata^ other 
than the groups previously dealt with, as showing direct indications 
of an archimerically segmented mesoderm, with the other primi- 
tive characters cited. 
We now have to inquire what bearing the above facts can have 
upon classification. 
The Platylielminthes , Nemertea , and Nemathelminthes, all are 
groups or phyla of the Triploblcistica, which show more or less a 
monocytic condition of the mesoderm, and there is at present no 
evidence for regarding them as having degenerated from coelomate 
forms. The body-cavity of the Nematoda approaches in some 
respects a coelome, but more evidence is required. For con- 
venience sake, they may be placed together as Pseudo-ccela. The 
rest of the Triploblastica give evidence of either being archi- 
merically segmented or of having passed through an archimeric 
stage. 
Those which remain with the primitive characters narrated above 
may be included in one group, the Archi-coelomata , which would 
comprise the Echinodermata, Archi-chorda , Chcetognatha, Brachio- 
poda, Edoprocta, and possibly the Endoprocta and Rotifer a. From 
forms allied to the Archi-chorda , the Eu-chorda have been further 
differentiated by metameric segmentation and further elaboration 
of structure, whilst from forms allied possibly to the Chcetognatha 
and Brachiopoda have arisen the Annelida and Arthropoda, the 
further elaboration of structure in this case also involving meta- 
meric segmentation. Apart from this feature, the Archi-annelida 
* Cf. Shipley, A. E., Quart. Journ. Micros. Sci., xxxi. There are difficul- 
ties in the way of this author’s comparison of Phoronis and Phymosoma. If 
we accept his comparison in figs. 31 and 32, then the pre-oral lobe must be 
looked for, not as indicated by Mr Shipley, on the anal side of the tentacles, 
but on the oral side, where the epistome is found in Phoronis. 
t Traiti de Zoologie Concrite , vol. v. 
