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- 
tne univalve .Mol- podsA, portion of odontophore, or “tongue," of Vel- 
1 -I fl C *1 utina, enlarged; B, portion of odontophore of Whelk 
1USKS, Or tile bliaiJS, ( Buccinum undatum), magnified — the entire tongue 
i crpn pro 11 a- 1 i r» rrn Q1 has 100 rows of teeth ; c ? hiead aud Odontophore of Lim- 
ik. llugUdJ, pet (p a t e u a V ulgata) ; D, portion of same, greatly mag- 
i. e.) it Consists of 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 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 n 
per Jaw of a Whale ( Balcenoptera ), tlcal UOllOW tUDCS , in tne lat 
showing baleen-plates: a, superior £ er baleeil, Or whalebone, 
maxillary bone; b, ligamentous gum ’ . 7 7 
attaching the horny body of the ba- plates, triangular in shape, and 
leen-plate, c; d, fringe of bristles; e, . . , 
smaller plates. fringed on the inner side, hang 
5 
