264 
II. L. M. I’lXKLL. 
champs states that in this species they do appeal' to vary 
particularly, but gives as the highest recorded by anyone : 
12 1 
13 
6 1 
7 
This is a great deal lower than the average number of sixty 
in Ph. vancouverensis, and such an anatomical charac- 
teristic seems to be of far more importance from a systematic 
Text-fig. 5. 
Longitudinal section through the base of the lophophore approxi- 
mately in the median dorsal lines. ( X 100.) 
])oint of view than such variable details as size and number 
of tentacles. Both Cori (3) and Selys Longchamps (14) point 
out that within limits the number of fascicles of longitudinal 
muscles is constant. 
The diaphragm or transverse septum (Fig. 5, d) slopes up- 
wards from the oral to anal side, meeting the dorsal surface 
just in front of the anal papilla. The two layers of perito- 
neum covering it are widely separated at the sides by the 
basement membrane, ivliich is continuous ivith that of the 
body-wall near the lower border of the nerve-ring, but 
towards its centre this median layer of the septum is so thin 
