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small, the effect being, as a writer describes it, 

 very much the same as if l instead of dragging 

 a harrow over the surface of a field, we were to 

 turn the harrow points upwards and .then drag 

 the field over the harrow ' ! * 



The resulting wear and tear of the anterior 

 teeth is continually made good by the incessant 

 development of new teeth formed in a sort of sac 

 in which the hinder end of the strap is lodged. 



In addition to this chain-saw-like motion the 

 odontophore has a scraping action, more or less 

 in a circular direction, whereby the shells of 

 other creatures are gradually bored. 



If the radula of a limpet or whelk freshly 

 extracted be drawn across the hand, the teeth 

 can be plainly felt. 



Now as to the disposition of the teeth on the 

 radula. The arrangement as well as the number 

 of teeth vary in the different representatives of 

 the Gasteropoda. The teeth are almost invariably 

 disposed in a kind of pattern like the longi- 

 tudinal rows of colour in a piece of ribbon (for 

 the teeth are beautifully coloured, even apart 

 * Cambridge Natural History. 



