HOW ANIMALS EAT. 
65 
Ftg. 29.— Teeth and Masticatory Apparatus of Gastero¬ 
poda : A, portion of odontophore, or “ tongue,” of Vel- 
utina, enlarged ; B, portion of odontophore of Whelk 
(Buecinum undatum), 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¬ 
ly a saw-cut. 
The dentition of 
the univalve Mol- 
lusks, or the Snails, 
is generally lingual, 
i. 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 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 p 11 . n ' n fLp lo+- 
per Jaw of a Whale ( Balcenoptera ), tlca ! HOllOW tUDeS , in tne ml 
showing baleen-plates: a, superior {- er baleen, Or whalebone, 
maxillary bone; b, ligamentous gum ’ # 1 7 
attaching the horny body of the ba- plates, triangular in shape, and 
leen-plate, e; d, fringe of bristles; e, . , . . , , 
smaller plates. fringed on the inner side, hang 
5 
