.OCEAN LIFE. 43 



any nutritious molecules, or minute living creatures, that may 

 happen to be present in the circumscribed space over which this 

 singular casting-net is thrown, and drag them down into the 

 vicinity of the mouth, where, being seized by the jaws, they are 

 . crushed and prepared for digestion. No sense but that of touch 

 is required for the success of this singular mode of fishing ; and 

 the delicacy with which the tentacula perceive the slightest con- 

 tact of a foreign body, shows that they are eminently sensible to 

 tactile impressions." 



CONCHIFEBA. 



" MOLLUSCOUS animals enveloped in a shell composed of car- 

 bonate of lime, forming two valves, connected by a joint, and 

 applied the one to the right, the other to the left side ; mantle 

 two-leaved, more or less open ventrally, generally with two orifices 

 behind ; gills four-leaved, no head, mouth placed at the angle of 

 the gills, furnished with lips and palps, sexes distinct ; young 

 undergoing a metamorphosis." 



" The great majority of Molluscs which inhabit bivalve shells 

 constitute a very numerous and extensive class, distinguished 

 by certain characters possessed by them in common. Encased 

 in dense and massive coverings of such construction as to pre- 

 clude the possibility of their maintaining more than a very im- 

 perfect intercourse with the external world, and deprived even of 

 the means of communication with each other, we might natu- 

 rally expect their organization to correspond in its general feeble- 

 ness with the circumscribed means of enjoyment and limited 

 capabilities of locomotion allotted to them. Numerous species, 

 indeed, are from the period of their birth firmly fixed to the rock 

 which gives them support, by a calcareous exudation that cements 

 their shells to its surface, as is familiarly exemplified in the case 

 of the common Oyster ; or else, as the Muscles anchor themselves 

 securely and immovably by unyielding cables of their own con- 

 struction. The Scallop, unattached 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 



