CONCHIFERA. 



255 



limited capabilities of locomotion allotted to them. 

 Numerous species are, from the period of their birth, 

 firmly cemented to the rock that gives them support, 

 as is familiarly exemplified by the common Oyster, 

 or, else, as the Mussels anchor themselves securely, 

 by unyielding cables of their own construction. The 

 Scallop imattached, but scarcely better adapted for 

 changing its position, rudely flaps together the 

 valves of its expanded shell, and thus, by repeated 

 jerks, succeeds in effecting a retrogressive movement ; 

 wliile the CocMes, destined to burrow in the sand, 

 are furnished with a tongue-like foot, by means of 

 which they dig holes, wherein they lie concealed, or 

 crawl, or even leap about upon the shore. Many, as 

 the Pholades, penetrate the solid rocks, and stones, 

 and excavate therein the caverns they inhabit, or, 

 as in the instance of the Teredo, with dangerous 

 industry, bore into the bottoms of ships, or submerged 

 wood of any description, and silently destroy, by their 

 perfidious ravages, the piers or chkes that human 

 labour has erected. The general structure of these 

 animals may be readily understood by examining 

 any of the species common in our markets. We 

 will select 



The Scallop {Pecten) for special description. On 



Fig. 193.— scallop. 



