258 THE VOYAGE OF H.M.S. CHALLENGER. 



with an asymmetrical incision, and that the different polymorphous appendages are 

 attached in regular order to the peripheral convex margin of their discoidal sac. This 

 margin is divided by a series of equidistant radial constrictions into a number of roundish 

 polygonal or quadrangular facettes (ten to twenty or more). Each articular facette is 

 surrounded by a promiuent muscular wall or frame, and bears a single large palpon with 

 its palpacle, and beyond it is attached a single siphon with its tentacle ; in the interval 

 between them is a pair of gonodendra, a proximal female and a distal male. The cormidia 

 are, therefore, perfectly ordinate, and succeed one to another regularly in the subhori- 

 zontal ventral median line of the depressed trunk of the siphosome (compare figs. 9 to 13). 

 The observations of Sars (already made in 1857) were twenty years afterwards confirmed 

 and more fully carried out by Claus (in 1878, 74, Taf. iii. figs. 1-4). Moreover, 

 Gegenbaur had already (in 1859) described in Stephanospira the spiral twisting of the 

 discoidal inflated trunk, and the regular order in which the siphons and the paired 

 gonodendra (a male and a female) were attached to the peripheral margin of the spiral 

 disc ; hence he derived its name. The spiral twisting in the siphosome of all Discola- 

 bidaa seems to be dexiotropic, opposite to the Inotropic spiral of the nectosome ; Claus, 

 who calls the former also lseotropic, seems to have confounded the proximal and the distal 

 part of the spiral (74, p. 13). 



Cormidia. — The numerous ordinate cormidia which compose the siphosome of the 

 Discolabidse, are disposed along the ventral median line of its trunk not less regularly 

 than in the Apolemidaj and the polygastric Calyconectse. The only difference is, that 

 the naked internodes are in the latter very long, in the former very short ; but they are 

 sharply marked by the limits of the facettes, or the basal insertions of the single groups 

 of medusomes. The effective cause of that difference is the divergent development of the 

 trunk of the siphosome ; this is tubular and much prolonged in a vertical direction in the 

 Apoleniidse, as in the Agalmidse ; it is vesicular, much shortened and inflated, and coiled 

 up spirally in a subhorizontal direction in the Discolabidse, as in the Nectalidse. The 

 trunk of the latter possesses, therefore, permanently about the same shape which the 

 trunk of the former exhibits only in the state of the strongest contraction. 



The composition of the ordinate cormidia is in all the three genera of Discolabidse 

 essentially the same. Descending from the proximal or apical (superior and external) face 

 of the trunk, towards the distal or basal (inferior and internal) face, we find successively 

 the following parts : — (1) a large palpon with its palpacle; (2) a female gonodendron ; 

 (3) a male gonodendron ; (4) a large siphon with its tentacle. Sometimes the number of 

 palpons is doubled, so that a pair of them (a larger superior and a smaller inferior) belong- 

 to each cormidium ; but it seems that this duplication is often accidental, and variable in 

 one and the same species. 



SipJions (PI. XX. figs. 13, 16, s). — A single large polypite is attached to the distal side 

 of each cormidium, and occupies therefore the innermost place on the subhorizontal basal 



