Feeding and Breathing 43 



a row and about 110 rows = 12,210; the little Fresh- 

 water Limpet (Ancyhis fliiviatilis) h has 120 rows 

 of 75 = 9000; and the Amber Shell {Succinea jiutris) 

 c of our watersides has 50 rows of 65 teeth = 3250. 

 A Mexican species of Helix is said to have 40,000 

 teetli, whilst UinhreUa, a Mediterranean moUusk, 

 has so many it is impossible to count them, but they 

 have been estimated to number souiewhere about 

 750,000 1 Every one of these minute teeth has 



a 



Teeth of radula of — a, Limncea stagnalis ; b, Ancylus fluviatllis; 

 c, Si(cd/ie« pu^m (greatly magnified) 



muscular attachment to the radula, and can be 

 erected or depressed at the will of the mollusk. 



These remarkable organs extracted from the 

 mouth of any of the common mollusks of our 

 hedges or seashores, make beautiful objects for the 

 microscope ; but their preparation requires a good 

 deal of care and nice manipulation. They are first 

 boiled in caustic potash to get rid of the animal 

 matter, and after washing in clean water are 

 mounted in glycerine jelly. 



Most of the mollusks that bear these radul?e are 

 also provided with salivary glands, and in some of 

 the species that habitually bore through the shells 



