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 
the univalve Mol- 
lusks, or the Snails, 
is generally lingual, 
i. e., it consists of 
microscopic teeth, usually 
Fig. 2U. —Teeth and Masticatory Apparatus of Gastero¬ 
poda : A, portion of odontophore, or “ tongue,” of VeU 
utina , enlarged ; B, portion of odontophore of Whelk 
(Buccinum 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. 
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, horn} 7 
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- 
per Jaw of a Whale (Balamoptera), ^ICal hollow tubes , 111 the lat- 
showing baleen-plates: a, superior t t } le baleen, 01’ whalebone, 
maxillary bone; &, ligamentous gum ' # 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 
