HOW ANIMALS EAT. 



65 



movement is given 

 to the horny ridges, 

 so that the "bite" 

 of the Leech is real- 

 ly a saw-cut. 



The dentition of „ .......... 



Fig. 29.— Teeth and Masticatory Apparatus of Gastero- 

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

 iiti?ia, enlarged ; B, portion of odontophore of Whelk 

 lllSKS, Or the feliaiJS, (Buccinum undatum), magnified — the entire tongue 

 j| y 1 has 100 rows of teeth ;C. head and odoutophore of Lim- 



1S generally lingual ? pet (p a tellavulgata) ; D, portion of same, greatly mag- 

 i 6 it Consists of nifie( ^» to s h° w tne 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 Slug 

 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- 



Fig. 30. — Section of one half of the Up- .» i i n ± \ n i . 



per Jaw of a Whale (Balcenoptera), tical hollow tubes J in the lat- 

 showing baleen- plates: a, superior t the baleen, Or whalebone, 

 maxillary bone; b, ligamentous gum > ' 



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



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



smaller plates. iringed on the inner side, hang 



5 



