OCEAN LIFE. 45 



glands be kept up without remission during the enlargement of 

 the shell, the lines upon its surface are continuous and unbroken ; 

 but if the pigment be furnished only at intervals, spots or colored 

 patches of regular form, and gradually increasing in size with 

 the growth of the mantle, recur in a longitudinal series wherever 

 the paint-secreting glands are met with. 



" The organs of hearing consist of a pair of transparent cap- 

 sules filled with a clear fluid. Each contains a glassy globule, 

 which constantly maintains a very singular and rotary motion, 

 that instantly ceases when the capsule is ruptured. These cap- 

 sules are situated in the foot. 



" Organs of vision are much more obvious, at least in many 

 species, being often highly colored, very numerous, and promi- 

 nently situated." 



GASTEROPODA. 



" MOLLUSCOUS animals furnished with a distinct head, and a 

 fleshy crawling foot ; either naked or protected by a shell, for 

 the most part formed of a single piece, and generally spirally 

 turned; mouth provided with lips, and a ribbon-like tongue, 

 armed with rows of teeth ; eyes two ; tentacles two or four. 

 Young subject to metamorphosis. 



" Extensively distributed over the surface of the land, or in- 

 habiting the waters either fresh or salt, there exists a very nu- 

 merous body of Mollusca, differing widely among themselves in 

 construction and habits, but distinguished by a peculiar locomo- 

 tive apparatus common to the entire class, by means of which 

 they are able to fix themselves to plane surfaces, and to move 

 from place to place by a slow or gliding motion. The Slug, the 

 Snail, the Limpet, and the Whelk, afford familiar examples of 

 their general form and appearance. 



" The upper parts in the majority of species, are covered with 

 a fleshy cloak or mantle, the edges of which are free, in a greater 

 or less degree, and in some cases are expanded into great lateral 

 wings. In the Sea-hare (Aplysia), these expansions serve, by 



