•J32 



RADIATA. 



Class IV. BISCOPIIORA. 



This term is from tlie Greek dlskns, a disc, antl phcro, to bear, and alludes to the general form of 



the animals belonging to this class. They bear the popular names of 



r^ ^^^ Jelly-Fisiies and Sea-Blubbers, from their gelatinous nature, and 



J^ "^^^^Sl^ Sea-Nettles, from the stinging sensation they have the power of pro- 



jT^ ^^^^^^ ducing when touched ; the term Acalephce, which has been generally 



applied to them, lias this signification. They are exclusively natives 

 of the ocean, which teems with them, from the intertropics to the 

 polar circle. Among the strange and beautiful creatures which 

 tenant the thronged and populous waters of the sea, they exhibit 

 sometimes the most fantastic, sometimes the most elegant figures, 

 adorned with colors of surpassing richness ; nor is their variation in 

 size less striking than that of their forms. Some are so minute as to 

 require the aid of a microscope, in their examination; others form 

 lar'>-e masses, which, as they float on the waves, cannot but attract 

 attention. Many shine with phosphorescent brilliance ; as the 

 vessel plows the briny water, or the oars of the boat throw up the 

 spray, when darkness covers the face of the deep, they glitter like 

 a shower of stars, and falling again, are lost in a sea of effulgence. 

 Some appear in the depths like balls of glowing metal ; some move 

 with an undulating course, appearing as they pass like a ribbon of 

 flame ; others like diamonds gem the rocks or the fronds of sea- 

 weed ; some float in shoals, displaying the lovely tints of the rain- 

 bow ; while others, like orbs of silver, glitter as they float on the 

 rolling current. They appear to be of a homogeneous and gelatinous 

 consistence, but in reality are composed of filmy tissues, disposed in 

 a cellular manner, and inclosing an abundance of sea-water, which, 

 when they are left dead on the beach, soon dries up, leaving only a 

 little scum or gummy web behind. 



"In walking along the sea-beach," says Dallas, "as the tide is 

 falling, the attention of the wanderer is often attracted by the number 

 of singular gelatinous masses left on the sands. At first sight it 

 would never be suspected that these are really living animals endowed with a structure of con- 

 siderable complexity ; but a very little examination will soon show the observer that this is the 

 case. If one of these lumps of jelly be put into a clear pool or basin of sea-water, parts, before 

 confounded in a shapeless mass, immediately unfold themselves ; a circular, umbrella-like disc, 

 surrounded by numerous short filamentous tentacles, appears to support the creature at the sur- 

 face of the water ; and from the center of this, depend four long arms with 

 membraneous fringed margins. This is the Medusa aiirita, one of the com- 

 monest species, and must have been often observed by those who frequent 

 the sea-shore. In the water the creature swims along most gracefully by 

 the contraction and dilatation of its transparent disc." 



All the animals of this class present a structure very similar to this. They 

 all possess a disc of greater or less convexity, which is employed, in the 

 manner already described, for the purposes of locomotion ; and in most of 

 them the margin of this disc is furnished with tentacles or cirri. The disc, or umbrella, consists 

 of two membranes, of which the lower is called the sub-umbrella. In the center of this the mouth 

 is situated, sometimes at the extremity of a peduncle of variable length, which contains the 

 stomach, and in some cases also the ovaries. The mouth is most frequently furnished with ten- 

 tacles. Some genera, although provided with a large peduncle or with tentacles, are said to have 



\ 



THE PELAGIA LABICUE. 



THE UEDUSA ALRITA. 



