9 6 



THE FOOD OF ANIMALS 



the "tongue" or "palate", and will usually be found described 

 as such in catalogues of microscopic objects. It is of importance 

 in classification, for the teeth vary in number, nature, and arrange- 

 ment in different species. 



SNAILS AND SLUGS (GASTROPODA) 



From Cephalopods we pass on to the enormous group of 

 Snails and Slugs, i.e. to the Gastropoda, of which vast numbers 

 are carnivorous. It is interesting to note that by cursory inspec- 

 tion of the empty shell it is pos- 

 sible to tell whether the inhabi- 

 tant subsisted on animal or vege- 

 table matter, for in the former 

 case the opening or mouth is 

 notched, in the latter continuous 

 or entire. The notch is for the 

 protrusion of a tubular organ 

 (the siphon) related to the breath- 

 ing function, and which will be 

 described in a subsequent section. 



Fig. 377.-A single row of Teeth from radulae of Carni- The tCCth in the radula of a Car- 



vorous Snails (greatly enlarged) 



A, From Glandina (a land-snail). B, From Whelk HlVOrOUS gastropod are USUally 



(Bncctnum undatum). On the right is shown the entire comparatively fe W and Specialized, 

 radula (natural size). ' 



Their form is often strongly 

 curved, or it may be hook-like (fig. 377). 



One of the commonest and most voracious inhabitants of the 

 zone between tide-marks round the British coasts is the Purple- 

 Shell (Purpura lapillus] (fig. 378). This is possessed of a pro- 

 trusible snout, armed with a strong odontophore, and it plays 

 havoc with other Gastropods and with Bivalves, especially mussels, 

 These may either be attacked through the opening of the shell, 

 or, failing this easy path, the Purple -Shell bores through the 

 firm investment of its prey. One commonly picks up the loose 

 shells of small bivalves in which a neat round hole has been 

 drilled, and as often as not this has been the work of a Purpura. 

 These snails may also be found crawling about projecting rocks 

 studded with acorn barnacles, the firm shells of which they per- 

 forate in much the same way and with the same object in view, 

 and a little careful observation will often result in the detection 



