MOLLUSKS. 



149 



containing the stomach and viscera, (2) without a radiate structure, 

 and (3) without articulations. The animals of the Oyster and Snail 

 are examples. In some kinds there are eyes and arms, but the 

 arms or appendages are never jointed; and in this the species are 

 distinct from Articulates. 



Figs. 157-159. 



,4° 



'■MS 



Eadiates. — Fig. 157, an Echinus without its spines, — the Clypeus Hugi of the Oolite ; 158, 

 the living Pentacrinus Caput-Medusa? of the West Indies (X %); a > &> c , ^ outline of the 

 stem of different species of Pentacrini ; 159, plates composing the body of a Crinid, Acti- 

 nocrinus longirostris Hall. 



Figs. 160 to 168 represent some of the kinds of Mollusks. Figs. 

 160, 163, 164, 165, are shells of different species ; 166, the shell of a 

 snail, with its animal ; 168, another shell, the Nautilus, with its 

 animal ; 162, a magnified view of a minute coral, with the living ani- 

 mals projecting from the cells, which, although apparently radiated 

 like a polyp, are still Mollusks, because this radiation is only exter- 

 nal, as is apparent in fig. 162 a, which represents one of the animals 

 taken out of the cell and more magnified. Fig. 169 is another 

 Mollusk, — a Cephalopod, — having some resemblance to the Eadiates 

 in the position of the arms, but none beyond this. 



The name Mollusk is from the Latin mollis, soft. The shells are 

 for the protection of the soft, fleshy bodies. 



III. Articulates. — Consisting (1) of a series of joints or segments, 

 and (2) having the viscera and nervous cord in the same general 

 cavity, but (3) having no internal skeleton ; as Worms, Crustaceans, 

 Insects. 



