CONNECTION BETWEEN THE SHELL AND ANIMAL. 113 



in truth after the fashion of the maker's mind, and little in 

 accordance with what a sober survey of the reality discloses. 

 This is not less beautiful nor less designed, but so far from 

 rising on the spectator, like alpine scenery, the more perfect 

 as he ascends, it lies wide before him with all its variety 

 level to his gaze, and perplexing by its unpatterned intri- 

 cacy. In every, or nearly in every, class or order, there are 

 some families which swim whithersoever it listeth them, 

 some which crawl or trail themselves along the solid gi*ound, 

 some which burrow and which confine themselves to their 

 narrow cells ; and others there are which have no power of 

 changing their sites, but live and die on their natal spot. 

 Instead therefore of making each class pass in separate re- 

 view before you, exhibiting, in a coloured glass, their pro- 

 gressive rise in motive capabilities, I rather choose to leave 

 system for the present; and, grouping, somewhat loosely, the 

 molluscans into the swimmers, the crawlers, the burrowers, 

 and the sedentaries, I will lay my illustrations before you 

 under these several heads. 



Before entering on the details, however, I must remind 

 you of the close connection between the shell and its inmate, 

 by which the former, instead of being a drag and hinderance, 

 becomes essential to the movements of the latter. The con- 

 nection between them is inseparable during life, and is 

 effected by the medium of muscles which go from the animal 

 to be inserted to the parietes of its dwelling. The mollusca 

 with bivalved shells are in this manner attached by one or 

 two large and powerful muscles, called sometimes transverse, 

 because, passing through the body, they are inserted into 

 both valves at opposite points ; and sometimes adductors, 

 because their office is to close the valves and keep them so in 

 opposition to the elasticity of the ligament at the hinge which 

 tends to separate them ; and the astonishing force with which 

 they act is well illustrated by the extreme difficulty of open- 

 ing those of an oyster. In the mollusca which are covered 

 with a shell in form of a case or sheath, as in some Pteropods 

 and Gasteropods, the animal is connected to the base of the 

 shell by a large dorsal retractor muscle. In simple conical 

 univalves, as the Limpet (Patella, Linn.), the body " is fas- 

 tened to the circumference of the shell by a ring of fibres, 

 which are attached all round the shell, and which, after pierc- 

 ing the outward covering or cloak, are inserted in the edges 

 of the foot, and interlaced with its circular fibres. Ante- 

 riorly they leave a free space for the passage of the head. 

 This muscle, by its contractions, brings the foot and the 

 shell closer together, and compresses the body; on relaxing, 



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