1895 - 96 .] Mr Arthur T. Masterman on Phoronis. 
63 
collar cavity. All the cavities tend to be obliterated by mesen- 
chymatous tissue. 
Trunk Cavities. — The longitudinal muscles run from septum to 
base, and are inclosed in special parts of the cavity, shut off by 
thin walls, from the general cavity of the coelome. The trunk cavity 
is bent upon itself, but this reduplication does not affect the collar 
or epistome regions. 
As regards the vascular system, the dorsal vessel runs in the 
space between the gut and the body cavities, and the ventral 
vessel evidently belongs to the space in the ventral mesentery, 
but is secondarily deflected over to the left coelomic cavity. 
Coming to the affinities of Phoronis , I am led to formulate the 
view that this genus must take its place amongst the Hemichordata , 
in spite of the obvious fact that in none of the known species have 
a notochord or gill-slits been described. 
In his report upon Phoronis buskii , Professor M £ Intosh was led 
to compare several of the organs, such as the nervous system, with 
those of Cephalodiscus, and he even suggested comparisons with 
Balanoglossus. Mr Harmer, in his Appendix to the Challenger 
Report upon ‘ Cephalodiscus ,’ also suggested some points of resem- 
blance between this form and Phoronis ; and Professor Lankester, 
in his article in the Encyclopaedia Britannica upon * Polyzoa ,’ 
pointed out features in common between the Pterobrachia and the 
Yermiformia. We can accept this observer’s comparison between 
the forms here mentioned without following him in his consti- 
tution of the Polyzoa or the Podaxonia. 
The formation of the group Hemichordata , involving the 
removal of Cephalodiscus and Rhabdopleura into phyletic con- 
nection with Balanoglossus , tended, to those who accepted this 
classification, to disguise what I believe to be the true affinities 
of Phoronis ; especially because the presence of a notochord and 
gill-slits were stated to be essential characters of the group. This 
is not the place to go fully into the views held with regard to 
the affinities of Phoronis ; various workers have allied it to the 
Gephyrea , the Brachiopoda , the Chcetopoda, or even the Polyzoa. 
I have embodied my main points of comparison of Phoronis 
with the Hemichordata in a table, all details being left over for 
the present. We may here deal with the two chief points in 
