68 COCKLE. 



a number of glittering studs of metallic brilliancy, 

 which are supposed to be eyes and at least are the 

 only representative of those organs observed in the class, 

 whose habits little require such a provision. Within 

 the mantle are found the branchiae or lungs, which 

 consist of four delicate leaves formed of radiating fibres 

 of extreme fineness. The mouth is a simple orifice, 

 bordered by membranous lips, and placed at one end of 

 the body, between the two inner leaves of the branchiae. 

 A great portion of the body consists of an extremely 

 firm muscle, round which the stomach, liver, and other 

 parts, are disposed, and which connects the two valves 

 of the shell together ; by its expansion allowing them 

 to open, and causing them to close by its contraction. 

 This most powerful muscle alone keeps the shell closed ; 

 and its strength must be familiar to every one who has 

 opened an Oyster, whose resistance to the knife ceases 

 only when this muscle is cut asunder. 



Such are the general features of the more simple 

 conchiferous animals, as the Scallop and Oyster. If 

 we examine the Cockle, we shall find some modifica- 

 tions, and the full development of a highly-organized 

 muscular foot. This organ exists but in a rudimentary 

 form in the Scallop, whose habits suggest other modes 

 of locomotion than those of running and leaping. The 

 Scallop, which inhabits deep places, where it lies on a 

 rocky or shelly bottom, swims or flies through the water 

 with great rapidity, moving itself by suddenly opening 

 and shutting the valves. In the Cockle the first differ- 

 ence which strikes us is, that the edges of the mantle 

 are not open all round, as in the Scallop, but united 



