530 



DISCOPHGRA. 



like disc, convex above and concave below, which forms the 

 upper part of the animal. It is by the continual contraction of 

 this disc, as they float in a somewhat oblique position, that the 

 animals are enabled to swim slowly through the water, and it is 

 from this circumstance 

 that their old name of 

 Pulmograde Acalephce 

 was given to them. The 

 texture of these curious 

 creatures is perfectly 

 gelatinous, and usually 

 transparent or translu- 

 cent, whence the names 

 of "Jelly-fish" and "Sea- 

 blubber," which are com- 

 monly applied to them. 

 Their substance consists 

 of a tissue somewhat 

 resembling cartilage 

 (ANIM. PHYSIOL. 45); 

 but contains so little 

 solid matter, that a Me- 

 dusa, weighing several 

 pounds when alive, is FIG. 722.-PELAGIA. 



reduced nearly to as 



many grains when dried. The fluid, which differs little, if at 

 all, from sea-water, gradually drains away, leaving but a thin 

 pellicle incrusting the surface on which the mass was placed. 

 Nevertheless these animated masses of sea-water exhibit a 

 greater complexity of organisation than we should have expected 

 from their gelatinous appearance ; and their beauty, when seen 

 swimming near the surface in a bright day, is very great. They 

 contain an abundance of thread- capsules, and many are even 

 capable of stinging the human skin with these curious weapons, 

 whence the name of " Sea-nettle " by which they are known in 

 various countries. The name Acalepha, formerly applied to them 

 in common with the other free-swimming gelatinous Radiata 



