96 F. W. GAMBLE, M.SC, AND J. II. ASHWORTH, B.SC. 



The musculature of the buccal mass consists of a strong sheath of 

 fibres derived from the longitudinal layer just behind the first 

 diaphragm. This sheath, which is loosely attached to the proboscis 

 by slips which run through the coclomic space between the two 

 structures (PI. VIII. Fig. 6, B. Sh.), is inserted into the anterior part 

 of the proboscis. Pressure of the coelomic fluid at this point causes 

 eversion of the buccal mass, which is withdrawn by the contraction 

 of its muscular sheath. 



The prostomium is retracted by a small sheet of muscle which ai'ises 

 partly from the longitudinal layer dorsally, and partly from the 

 muscular covering of the circumossophageal connectives ventrally, 

 and it is inserted into the ventral surface of the brain, and the ventral 

 and hinder edge of the nuchal organ (PI. VIII., Fig. 6, Nu. Tr.). 



The parapodial muscles are modifications of the longitudinal layer. 

 One, the retractor of each notopodium, is remarkably long, reaching 

 to the side of the nerve-cord (PI. VIII., Fig. 13, /in.). The protractors 

 (Pn.) of the notopodia are six to eight in number, three to four being 

 placed in front of, and three to four behind, the setigerous sac. They 

 arise from the bod}'- wall just below the dorsal longitudinal vessel, and 

 are inserted into the base of each sac. 



The position and relations of the three anterior septa or diaphragms, 

 of the dorsal and ventral mesenteries between the first two of these, 

 and the presence of regularly arranged septa in the tail region, have 

 already been noted. It may be added that a pair of outgrowths from 

 the first diaphragm lie under the oesophagus, opening anteriorly into 

 the coelomic space in front of the first septum. They are very vascular, 

 and contract rhythmically every three or four seconds during life, and 

 are doubtless of use in everting the proboscis (PI. VII. and VIII. Figs. 

 5 and 6, Dph. Ph.), 



hi the caudal region the intestine is attached both above and below 

 to the body-wall by mesenteries, in which the dorsal and ventral 

 vessels lie. 



5. Alimentary Canal (PI. VII.). 



This consists (1) of an eversible buccal mass (Bucc. M.), of a pinkish 

 or greenish-brown colour, which lies in front of the first septum ; (2) 

 of an oesophagus, of a light brown colour, provided with a pair of 

 glandular pouches behind the third diaphragm; (3) of a gastric region, 



