56 



SHELLS AND SHELL-FISII. 



observes, "an elongated proboscis. Their tongue/' he 

 continues. " is armed with little hooks^ which, by slow 

 and repeated rubbings, act upon the hardest bodies." 

 It is by this process that they perforate, with the 

 smoothness and precision of an auger, the shells of 

 other animals, which they then destroy and suck the 

 juices of. The sexes are always separate; and the 

 aperture of the shell, in most instances, is closed by an 

 operculum. The various modern genera formed out 

 of the Linn^an Murex, Buccinum, Conns, Voluta, &c., 

 are included in this tribe, the shells of which are 

 always spiral, and furnished with a notch or emargin- 

 ation at the base. 



(48.) The Phytophaga, as the name implies, are 

 feeders upon plants ; for although several, like the 

 slugs, will devour animal substances, they more habitu- 

 ally live upon vegetables. They are, besides, eminently 

 distinguished from the carnivorous race by two cha- 

 racters : their mouth does not form a proboscis ; and the 

 aperture of their shell is entire, — in other words, without 

 the notch or canal for the passage of the siphon (when 

 it exists), so universal in the last group. In all but 

 one or two genera, as the slugs and the marine OncliidcE, 

 they are more or less covered with shells, which, 

 m however small a degree, are always spiral. By far 

 the greater part of them have the sexes separate ; but in 

 regard to all the other organs connected with respiration, 

 they may be said to vary in every possible way, — a clear 

 proof that such variations, in groups naturally and 

 closely allied, cannot be taken in an arbitrary sense. 

 Many of these animals have their branchia as in the 

 ZoophcKja; some few, as Cyclostoma and Helicina, even 

 according to J\I. Cuvier's admission (who places them, 

 nevertheless, with his Pectinibranchid), '' have instead of 

 gills, a vascular network covering the top of a cavity 

 that is otherwise similar ; and they respire, like the 

 Limaoc, the natural air.'' The whole of the terrestrial 

 slugs and snails, again, breathe through an open perfo- 

 ration under the edge of the reflected mantle, which 



