254 J. H. ASHWORTfl. 



the body-wall immediately dorsal to the level of the notopodial 

 setal sacs (figs. 14, 16). The nephridia are usually almost 

 hidden from sight beneath these oblique muscles. 



The parapodial muscles are moderately well developed 

 (fig. 9). Each bundle of setse is moved by (1) a number 

 (about five to eight) of slender protractor muscle strands 

 attached to the base of the setigerous sac and to the body-wall 

 near the level of the mouth of the sac, and (2) a few short 

 strands which pass from the base of the notopodial setal sac, 

 and are inserted into the base of the neuropodial sac. By con- 

 traction of the latter muscles the bases of the setal sacs ap- 

 proximate, and at the same time the distal ends of the two 

 groups of the setee are caused to diverge. 



Into the inner end of each lateral sense organ a special 

 retractor muscle is inserted. The other end of this muscle is 

 attached to the base of the notopodial setal sac (fig. 9). 



The position and arrangement of the four anterior dia- 

 phragms and the occurrence of small strands of connective 

 tissue, I'epresenting septa, accompanying the segmental 

 vessels in the post-branchial region of the body are described 

 below (p. 255). 



There is on each side a short muscle band arising from the 

 lateral body-wall and inserted into the inner and lower end of 

 the corresponding nuchal organ. On contraction this muscle 

 serves to retract the nuchal organ, and also, to a small 

 extent, the prostomium. The latter is well supplied with 

 muscles (fig. 15). 



There are several strong muscle strands passing from the 

 buccal mass to the neighbouring body-wall. These are the 

 retractors of the proboscis (fig. 14). 



Along almost the whole length of the stomach and intes- 

 tine there is an incomplete ventral mesentery, consisting of 

 numerous separate muscle strands passing from the ventral 

 wall of the stomach to the body-wall, close to the nerve-cord. 



9. General Anatomy of the Internal Organs. 

 Fig. 14 shows the appearance of the animal when opened 



