4 
THE VOYAGE OF H.M.S. CHALLENGER. 
oblong central nervous system, which gives off anteriorly a commissure surrounding the 
pharynx. 
The sexual organs are hermaphrodite. The female organs consist of a number of 
ovarian caeca, dorsal in position ; they open into the cloaca by a central uterine tube. The 
testes are usually ventral in position, and ramify on either side of the stomach ; the caeca 
Fig. 1. — Diagram of the Structure of Myzostoma. 
CyC\ o the 10 pairs of cirri; Cl, cloacal opening; i, intestine; M, mouth; N, central nervous system (blue), with n, n, 
oesophageal ring; ov, ovarian tubes (yellow); P r P 5 , the five pairs of parapodia ; Ph, protruded pharynx; R, the 
rectum ; SySi, the four pairs of suckers ; t, testicular follicles ; U, opening of the uterus into the rectum ; V, stomach ; 
i the two lateral male genital openings. 
unite on cither side into a spermatic vesicle, which opens to the exterior between the 
third parapodium and the margin of the body. 
The above description, with a few unimportant modifications, applies to all the species 
known up to the present time. I shall now show how far our knowledge of the anatomy 
of the group has been advanced by the new forms to be described in the present Memoir. 
