544 



GASTEROPODA. 



274 - 



(fig. 273, d d), if they do not act altogether, serve to bend it in any 

 direction, thus becoming the antagonists to each other. 



(1446.) In the internal cylinder are contained the tongue, with all 

 its apparatus (e e), the salivary ducts (/), and the greater part of the 

 oesophagus (</) ; but the principal use of the proboscis is to apply the 

 end of the tongue to the surface of bodies that the Buccinum wishes to 

 erode and suck. The tongue itself (e) is a cartilaginous membrane, 

 armed with hooked and very sharp spines. It is sustained by two long 

 cartilages, the extremities of which form two lips (c), that can be sepa- 

 rated or approximated ; or the cartilages can be made to move upon 

 each other by the mass of muscles in which they are imbedded. When 

 these cartilages move, the spines that cover the tongue are alternately 

 depressed and elevated; and by a repetition of similar movements, 

 aided perhaps by some solvent quality in the saliva, the hardest shells 

 are soon perforated by this singular file. 



(1447.) The salivary glands are 

 lodged in the visceral cavity, and 

 are composed of numerous secern- 

 ing ca3ca enclosed in a membra- 

 nous capsule (fig. 274, h, Jc) : their 

 ducts (g, e), which are necessarily 

 as long as the proboscis when ex- 

 tended to the utmost, open by two 

 apertures placed at the sides of 

 the spinous tongue (6). The oeso- 

 phagus (fig. 273, g g) runs along 

 the centre of the proboscis through- 

 out its entire length, and, when 

 that organ is protruded, becomes 

 nearly straight ; but when the 

 proboscis is drawn in, the oeso- 

 phagus is folded upon itself among 

 the viscera. 



(1448.) Just at the commence- 

 ment of the stomach there is a 

 small crop (fig. 274, /); and the 

 stomach itself is single, without 

 anything in its texture requiring 

 special notice, its lining mem- 

 brane being soft, and gathered 



into longitudinal folds (f). 



(1449.) Equally simple is the 



alimentary apparatus of the Heteropoda. In these the stomach (fig. 

 269, /) is a mere dilatation of an intestiniform tube. The intestine is 

 not lodged in the general cavity of the body, but, with the mass of the 



Alimentary canal of Si 



