314 



THE VOYAGE OF H.M.S. CHALLENGER. 



are numerous cirri which serve as tactile organs and organs of attachment; each parapodium 

 contains a hook-apparatus with a complicated musculature. The tree-like ramified 

 alimentary canal opens close to the anterior end of the body by the mouth, through which 

 the pharynx can be extruded; the anus is situated close to the hinder margin, and 



Fig. 125. — Diagram showing the Structure of Myzostwiia. 



Ci-C 10> the 10 pairs of cirri ; CI, cloacal opening ; i, intestine ; M, mouth ; N, central nervous system (blue), with n, 

 oesophageal ring ; ov, ovarian tubes (yellow) ; P,-P 6 , the five pairs of parapodia ; Ph, pharynx ; R, the rectum ; Sj-S-, 

 the four pairs of suckers ; t, testicular follicles ; U, opening of the uterus into the rectum ; V, stomach ; $ the two 

 lateral male genital openings. 



receives also the duct of the branched ovarian tubes. The male sexual organs consist of 

 two ramified testes which open on either side of the body by a separate opening. The 

 nervous system forms a compact ventrally situated ganglionic mass, from the anterior end 

 of which is given off a simple nerve ring enclosing the pharynx. This description holds 



