GASTEROrODA. 411 



their muscles, as well as a tongue covered with spines, and its 

 opening is guarded by two fleshy lips. The jaws form the basis of 

 all this apparatus : their substance is horny ; pi gt 190. 



their colour a yellowish brown ; and their form, 

 very extraordinary for an organ of this kind, 

 cannot be better described than by comparing 

 them to the shears used in shearing sheep. 

 They differ, however, in the following par- 

 ticulars : instead of playing upon a common 

 spring, the two blades are found to work 

 upon a joint, and, instead of being flat, they 

 are slightly curved. 



These two blades are very sharp, and there 



is nothing that has life that they cannot cut when the animal 

 causes the cutting edges to glide over each other. For this 

 purpose muscles of great strength are provided, the fibres of which 

 are transverse ; and their office is to approximate the two blades, 

 that are again separated by the natural elasticity of the articulation 

 whereby they are united at one extremity. 



The aliment, once cut by the jaws, is immediately seized by the 

 papillae of the tongue ; which, being sharp and directed backwards, 

 continually drag, by a kind of peristaltic movement, the alimentary 

 materials into the oesophagus. 



(447.) The fourth and most complicated form of the mouth is 

 found in the pectinibranchiate Gasteropods, and with its assistance 

 these animals can bore through the hardest shells in search of food ; 

 making a hole as round and smooth as if it had been made by a 

 drill of human contrivance. It is from Cuvier we again borrow 

 the subjoined description of this unique apparatus.* 



The proboscis of Buccinum is organized with marvellous arti- 

 fice : it is not simply provided, like that of the elephant, with the 

 means of flexion and extension, joined with a limited power of 

 contraction and elongation ; but it can be entirely retracted into 

 the body by drawing itself into itself in such a manner that half of 

 it which forms its base contains and encloses the half nearest its 

 point ; and it can protrude itself from its sheath thus formed, by 

 unrolling itself like the finger of a glove, or like the horns of the 

 garden snail, only it is never completely retracted, but always re- 

 mains more or less folded upon itself. 



It may be represented as being composed of two flexible cylin- 



* M6moire sur le grand Buccin (Buccinum undatum), et sur son Anatomic. 



