THE LUCEKNAKID^E. 



351 



and pigment-spots, here united into a single organ, termed the 

 lithocyst, are each protected externally by a sort of hood, whence 

 these jelly-fishes have been named " Stegonophthalmia," or 

 " covered-eyed," by Forbes, to distinguish them from the 

 naked -eyed " Gymnophthalmia," or Medusidae. The Pelagidae 

 (Chrysaora), which form one of the divisions of this group, are 

 simple, and have their margin surrounded with tentacles like the 

 Medusidae, while the Ehizostomidae have no marginal tentacles, 

 and consist of numerous polyps studding the trunks of a de- 



Oceanic forms of LncemandaE 1 .. 

 a, Rfiizostoma pulmo. b. Chrysaora hysoscella. c. Its llthocyit.— (All reduced.* 



pendent tree. These animals have consequently no central 

 mouth, but hundreds of little mouths all active for the welfare 

 of the community. 



The sessile Lucernaridae differ from the other members of 

 the order by the narrow disc or stalk which serves to fix their 

 body when at rest. Their quadrangular mouth is in the centre 

 of the umbrella expansion, and round the margin of the 

 cup arise a number of short tentacles, disposed in eight or nine 

 tufts in Lucernaria, and forming one continuous series in 

 Carduella. 



