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 



\* dufsisn 



B 



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

 the Univalve .Mol- pods: Af portion of odontophore, or" tongne," of Pel- 

 utina, enlarged ; B, portion of odontophore of Whelk 

 (Kuf-cinum undatitrn), magnified the entire tongue 

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

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

 nified, to show the transverse rows of siliceous teeth. 



lusks, or the Snails, 



is generally lingual, 



i. ., 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 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- 

 rftynchus) and Whalebone 

 Whale. In the former, the 

 plates consist of closely set ver- 



FIG. 30. Section of one half of the Up- , 1111 , i ,1 i , 



per Jaw of a Whale (Balcenoptera), tlCal hollOW tubes ; in the lat- 

 showiug baleen -plates: a, superior * pr *u p Kalppn nr wlialaHnnA 

 maxillary bone; ft, ligamentous gum -' IJ 3D > 



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



leen-plate, c; d, fringe of bristles; e, * . 7 



smaller plates. fringed on the inner side, hang 



5 



