SUB-CLASS SIPHONOPHORA. 75 



cliitinous covering or polypaiy. There may or may not be swim- 

 ming-bells or nectocalyces, and the tentacles arc very complicated 

 in structure, and often attain a gi'eat length. The ]jolypites present 

 no special points of interest, but are often furnished with the pro- 

 tective plates which have been already spoken of as "bracts." 



As a good exampile of the Phymjthorida', tlie Portuguese Man-of- 

 war may be taken (fig. 40, <i). It is comjjosed of a large spindle- 

 shaped float, often of several inclies in length, upon the under 

 surface of which are arranged a nundjcr of polyjjites, together with 

 highly contractile tentacles of great length, and re])roductive oigaus. 

 The Jentacles are richly furnished with thread-cells ; and it has the 

 power of stinging very severely. Pliysalia is commonly found float- 

 ing at the surface of tropical and sub-tropical seas. 



Another very beautiful mendjer of the Physaphoridn; is the VcleJla 

 vnlgaris, which occurs abundantly in many seas. It is about two 

 inches in length by one and a half in lieiglit. The proximal end of 

 the coenosarc is gieatly expanded and flattened out into an oval disc, 

 which carries a veitical ti'iangular crest, running obliquely across 

 its uj)per surface (fig. 40, h). The whole oi'ganism is semi-transpa- 

 rent and of a beautiful bluisli colour, and it floats at the surface of 

 the sea with the vertical crest exp)osed to the influence of the wind, 

 and thus officiating as a saik From the under sm-face of the disc 

 are suspended the various appendages of the organism, consisting of 

 a single large central polypite ; a numbei' of processes, like polypites 

 in shape, and carrying medusiform gonojdiores ; and lastly, a single 

 series of tentacles which arise from the caniosarc quite ir.dependently 

 of the polypites. 



