SUB-CLASS SIPHONOPHORA. 



73 



the bell is also furnished with a delicate ledge, which runs round its 

 circumference, and is known as the " veil." The structure, therefore, 

 of the nectocalyces, is very similar to that of an ordinary medusiform 

 gonophore, the chief difference being the absence in the former of 

 the central polypite or manubrinm. The nectocalyces are highly 

 muscular, and have the power of alternately contracting and dilat- 

 ing, thus driving the whole organism through the water. In I'l-ai/a 

 (fig. 39), which may be taken as a good example of the group, the 



- S 



Fiy. 39. — Oalyctri:hi:'Hd(e. A, Uiiper portion of the colnity of }'r0.ya mnxima, of the 

 natural size: ?i The iiroxiiiial nectocalyces; it'/t' Mouths of the same; c c Ca-no- 

 sarc, carrying polyjiites (p )>) at intervals, along with their swinniiii^g-ltells (.s .s) 

 the openings of these beinji indicated by the letters m m ; t Tentacles. B, A single 

 polypite of the same (/'), separated from the coMiosarc, and enlarged, with its swini- 

 nnng-bell (s), the opening of the bell (vi), and the tentacles (0- (Alter Gegenbaur.) 



nectocalyces (n) are succeeded by a series of polypites. Each poly- 

 ])ite (p) is furnished with a mouth, opening into a digestive sac, 

 which in turn communicates with the cavity of the crenosarc. In 

 this form each polypite has a little swimming-bell of its own ; but 

 in many forms each is protected b}' an over-arching plate, termed 

 a " bract." Each polypite has in gener-al a single tentacle, rising 

 from near its base, usually of gi-eat length, and provided with lateral 

 branches armed with numerous thread-cells. The reproductive oi-gans 



