iLPEiL — sept. 1858.] Order Radiata. 



125 



The family of the " Root-medusas" (Rhizostomida>) is better 

 known than the preceding. Under a bell-shaped covering are 

 seizing arms governed by the number 4, which are sometimes 

 branched, and at the ends of which are sucking apertures which 

 lead into a roomy stomach ; — see fig. 2, plate iv. There is no 

 mouth, and the vessels proceeding from the stomach form an ele- 

 gant net-work at the edge of the bill. The bodies on the edge 

 are of a bright red. Some genera of this family attain a diameter 

 of several feet. Rhizostoma, Cephea, Cassiopea. 



The family of the " Proboscis-medusae" (Geryonidm) has no 

 mouth, but under its bell-shaped disc a very moveable massive 

 stalk, in which rise six channels and open out into a six sided 

 little stomach. The bodies on the edge are also arranged accord- 

 ing to the number 6 and are colourless. The end of the proboscis, 

 where we find the six sucking apertures is sometimes in folds, 

 sometimes set with cilias ; — see fig. 3, plate iv. Geryonia, Favo- 

 nia, Saphenia, Lymnorea. 



As almost the whole class of the Medusas consists of soft gela- 

 tinous animals, we cannot expect to find their fossil remains, yet 

 some confused impressions in the slates of Sohlenhofen seem to 

 prove that the ancient seas were inhabited by Medusas. The little 

 trees also on which the bell-polyps are formed are too soft to have 

 left any traces. In the present day both forms of the class are to 

 be found in abundance in all seas, and are pursued by the Cteno- 

 phoroe by swimming snails which feed on them. The greater num- 

 ber shine by night with a trembling yellow light, which increases 

 in brilliancy when they are in motion. 



Class Siphonophora. 



This class is a strange mixture of curious animals, merely being 

 placed together in consequence of our extraordinary ignorance of 

 their organization. In fact we do not know whether they are to 

 be considered as simple animals with many sucking-apertures, or 

 as a swimming polyp-stock, on which common stem a number of 

 simple polyps are placed : — their anatomy is not understood, for 

 neither their nervous system, nor organs for seeing, breathing or 

 hearing have yet been found. 



