HOW ANIMALS EAT. 



65 



movement is given 

 to the horny ridges, 

 so that the "bite" 

 of the Leech is real- 

 ly a saw-cut. B 

 The dentition of _ 



FIG. 2W. Teeth and Masticatory Apparatus of Gastero- 



the Univalve Mol- pods: A, portion of odontophore, or "tongue," of Pel- 

 , , 4.1 o ] utina, enlarged; B, portion of odontophore of Whelk 

 IllSKS, Or tile OliaiJS, (Biuxinum undatum), magnified the entire tongue 

 i a rr ATI f>ra 1 1 v 1 i r> rrn a 1 nas 10 rows of teeth : C ; head and odontophore of Lim- 

 it? & t;il dUJ miglldJ, p et (patella vulgata) \ D, portion of same, greatly mag- 

 i. 6. it Consists of nifled, to show the transverse rows of siliceous teeth. 



microscopic teeth, usually siliceous and amber -colored, 

 planted in rows on the tongue. 

 The teeth are, in fact, the ser- 

 rated edges of minute plates. 

 The number of these plates va- 

 ries greatly ; the garden Sing 

 has 160 rows, with 180 teeth 

 in each row. 



All living Birds, and some 

 other Vertebrates, as Ant-eat- 

 ers, 24 Turtles, Tortoises, Toads, 

 and Sturgeons, have no teeth. 

 Their place is often supplied 

 by a horny beak, a muscular 

 gizzard, or both structures. 



In a few Vertebrates, horny 

 plates take the place of teeth, 

 as the Duck Mole (Ornitho- 

 rhynchus) and Whalebone 

 Whale. In the former, the 

 plates consist of closely set ver- 

 hollow tubes ; in the lat- 



r, the baleen, or whalebone, 



attaching the horny body of the ba- plates, triangular ill shape, and 

 leen-plate, c; d, fringe of bristles ; e, v . ' 



fringed on the inner side, hang 

 5 



smaller plates. 



