278 
H. 1,. M. PIXELL. 
Muscular Layers. — Tlie circular muscles are as usual 
(Fig. 13, c.oii.), aud a few radial muscles traverse the 
coelom, especially in the distal part of the body. 
The lougitudiiial muscles (Fig. 13, 1. m.) are very greatly 
developed. The fascicles are more numerous than in any 
other described species of the Phorouidea. 'I'he usual 
number in the region of greatest development, i . e . about 
50 mm. from the distal eud, is about 126. These lon<>-itudinal 
muscles are distributed as follows : 41 in the left oral 
chamber, 42 in the right, 23 in the left anal chamber, and 
20 in the right, or according to Longchamps’ formula — 
41142 
23 I 20 
126. 
The fascicles are pinnate in transverse sections, and may 
extend inwards to a distance of 160 /x. 
The nuclei of the peritoneum covering them are very pro- 
minent (Fig. 12, j>.). Between the muscles a fold of the 
peritoneum extends inwards for a short distance ; four of 
these folds are mncli longer, and reach the alimentary canal 
forming the mesenteries which divide the body cavity into the 
two anterior or oral and two ])osterior or anal compartments. 
The collar (Figs. 5, 7, 8, 9, 10, c.) contains no cadom, but 
consists of basement tissue with numerous small cells. The 
epithelium covering its outer side is columnar and similar to 
that over the general body surface {col. ep.), but at the tip 
and down the inner side it is replaced by small cubical cells 
(c?t. ep.). There are no muscles developed in connection with 
the collar, so that though it suggests the introvert of the 
Sipunculoidea and Polyzoa it is appai’ently quite functionless 
in that respect. Gilchrist (7) suggests that “ it is the 
remnant of an ancestral introvert whicli has been retained 
with the new function of protection of the nerve-ring.” 
The diaphragm (Figs. 8, 9, d.) is thin, but apparently con- 
sists of the usual three layers. I have seen it appear to 
branch owing to the emergence of a blood-vessel, which has 
evidently been running for some distance obliquely' across 
the region where the glandular la^mr of the nephridial funnel 
