SECT. m. CAMPANOGRADE ACALEPHAL. 103 



tusely octangular, with eight rows of cilia, extending 

 from a mouth at one end to a kind of ciliated star at the 

 other. The Beroes are of a gelatinous transparent sub- 

 stance, which expands and contracts with great facility : 

 it is always expanded when they swim. 



The Cestum Yeneris belongs to another genus of the 

 same family. It is like a blue ribbon, the mouth and 

 vent being on the opposite sides in the middle of the 

 band, which is furnished throughout its whole length 

 with active cilia for swimming. The ciliograde Hydrozoa 

 are monoecious, and do not produce medusa-zoids. 



Campanograde Acalephce. 



There is a group of oceanic Hydrozoa, consisting of 

 several families, which are fed by numerous suctorial 

 organs called polypites, with tentacula and thread-cells 

 attached to their bodies, so that they are analogous to 

 the marine hydrse, in being colonies of individuals 

 united into a compound animal. Some have air-vessels, 

 which enable them to float on the surface of the water ; 

 but the locomotive organs of this group are bells, so 

 that they may be called Campanograde Acalephse. 



The family of the Diphyidse are colourless, and of such 

 transparency that they are all but invisible when in the 

 water, and are gelatinous masses clear as crystal when 

 taken out of it. They are chiefly inhabitants of the 

 warmer parts of the Pacific and Atlantic Oceans, but 

 many fine specimens are found in the Mediterranean. 

 Of these the Praya diphys is one of the most extraordi- 

 nary (fig. 117). It has two large swimming-bells, their 

 mouths turned backwards, with which the whole com- 

 munity is connected. They are nearly equal in size, 

 soft, gelatinous, transparent, and colourless, rounded in 

 front, open and truncated behind. The adjacent sides 

 are parallel, with a groove between them, into which 



