29 



Class RADIARIA, or RAYED ANIMALS. 



"The firmament 



Was thronged with constellations, and the sea 

 Strewn with their images." — Jajies MoziTGoniiKT. 



Fig. 16.— SraB-Fisir. 



We have now reached the fourth, or highest class of the 

 radiated animals. In these the radiated structure is not con- 

 fined to the nervous system, or to the arrangement of the 

 parts surrounding the mouth: it extends to the form of the 

 hody, and is strikingly manifested in the common Jelly-fish, 

 or in any one of the various Star-fishes {Fig. 16) so abundant 

 on our coast. The two examples just mentioned point to an 

 obvious and very natural division of the class. The soft and 

 gelatinous tribes belong to a group of animals whose domain 

 is the wide and open sea; the Star-fish and the Sea-urchin, to 

 a community whose members feed upon garbage and shell-fish, 

 at fathomable depths. The integument or covering of each of 

 these groups of animals is suited to the situation which they 

 are destined to occupy. That of the gelatinous Radiaria is 

 soft and membranous; that of the other is hard, coriaceous, 

 and prickly; thus furnishing a defence against the perils 

 which those species must encounter whose habitat is on 

 coasts exposed to the violence of the ocean. To the former 

 of these two groups, distinguished, because of their stinging 

 powers, by the teiTu Acalephce, a Greek word signifying 

 nettles, our attention may in the first instance be directed. 



