HOW ANIMALS EAT. 



65 



Pig. 2H. — Teeth and Mnsticatory Apparatus of Gaster{)- 

 pods : A, portion' of odoutophoi^, or " tongue," of Vcl- 

 tittJid, enlarged ; B, portion of odontophore of Whelk 

 {Buccinum imdaiitm), magnified — the entire tongue 

 has 100 rows of teeth ; C. head and odontophore of Lim- 

 pet {Patella vulgata) ; D, portion of same, greatly mag- 

 nified, to show the transverse rows of siliceous teeth. 



movement is given 



to the horny ridges, 



so that the "bite" 



of the Leech is real- 



Jy a saw-cut. 



The dentition of 



the univalve Mol- 



lusks, or the Snails, 



is generally lingual, 



*. e., it consists of 



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 gi-eatly; the garden Slug 

 has 160 rows, with 180 teeth 

 in each row. 



All living Birds, and some 

 other Vertebrates, as Ant-eat- 

 ers," 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- 

 rkynckus) and Whalebone 

 Wliale. In the former, the 

 plates consist of closely set ver- 



iCiG. 30.— SectionofonehalfortbeUp- ,; 1 i,_i]^„ fnhps- in thp Int- 

 per Jaw of a Whale (BaUemptera), tlCal llOliOW tUDCS , m lUC lat- 

 showing baleen -plates: o, superior ^gj, j.Jjg balcCn, Or whaleboUe, 

 maxillary bone; b, ligamentous gum ' . , . , 1 



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

 leen-plate,<!; d, fringe of bristles; «, ^ . , ^i . •! i 



Bmaiier plates. fringed on the inner side, hang 



5 



