4 MANUAL OF ZOOLOGY. 



colour and semi-transparent, and it floats at the surface of the 

 sea, with its vertical crest exposed to the wind as a sail. 



DIVISIONS OF PHYSOPHORIDJE. (AFTER HUXLEY.) 



Fam. I. Apolemiadce. Hydrosoma with nectocalyces and hydrophyllia, 

 the latter united with the other organs into groups, which are arranged at 

 considerable intervals along the ccenosare. Ccenosarc filiform. Pneumatocyst 

 small. 



Fam. II. Stephanomiadce. Hydrosoma with nectocalyces and hydro- 

 phyllia, the latter arranged with the other organs in a continuous series. 

 Ccenosarc filiform. Pneumatocyst small. 



Fam. III. Physophoridce. Hydrosoma with nectocalyces, but without 

 hydrophyllia. Distal end of the filiform coenosarc dilated. Pneumaiocyst 

 small. 



Fam. IV. Athorybida. Hydrosoma without nectocalyces, but with hy- 

 drophyllia. Pneumatocyst occupying almost the whole of the globular 

 ccenosarc. 



Fam. V. Rhizophysiadce. Hydrosoma without either nectocalyces or 

 hydrophyllia. Ccenosarc filiform. Pneumatocyst small. 



Fam. VI. Physaliadce. Pneumatocyst occupying almost the whole of the 

 thick and irregularly fusiform ccenosarc. No nectocalyces or hydrophyllia. 



Fam. VII. Velellida. Hydrosoma without nectocalyces or hydrophyllia ; 

 with short, simple, or branched, submarginal tentacles. A single central 

 principal polypite. Pneumatocyst flattened, divided into chambers by 

 numerous concentric partitions, and occupying almost the whole of the 

 discoidal ccenosarc. 



CHAPTER X. 



DISCOPHOEA. 



SUB-CLASS III. DISCOPHORA (Acalephce* in part). Since 

 this sub-class contains only a single order, that of the 

 Medusidce, a single definition necessarily suffices for both. 

 The Medusidce are denned as ' Hydrozoa whose hydrosoma is 

 free cmd oceanic, consisting of a single nectocalyx, from the roof of 

 which a single polypite is suspended. The nectocalyx is furnished 

 with a system of canals. The reproductive organs are as pro- 

 cesses either of the sides of the polypite or of the nectocalycine 

 canals.' (Greene.) 



* The old sub-class of the Acalephfe contained the Grymnophthalmatc 

 Medusa ( = the Discopkora), and the Steganophthalmate Medusa ( = the 

 Lucernarida in part), the two being placed in a single order under the 

 name of Pulmograda. The Acalephce also contained the CtenopJiora and the 

 Calycophoridce and Physophoridfe, of which the former constituted the 

 order Ciliograda, whilst the two latter made up the order Physograda. The 

 Cteno'phora, however, are now generally placed amongst the Actinozoa, 

 whilst the Calycophoridce and Physophoridce constitute the Hydrozoal sub- 

 class Siphonophora. 



