HOW ANIMALS EAT. 63 
trituration of solid food. If wanting, the legs are often 
armed with spines, or pincers, to serve the same purpose, 
as in the Horse-shoe Crab; or the stomach is lined with 
“oastric teeth,” as in some marine Snails; or the deficiency 
is supplied by a muscular gizzard, as in Birds, Ant-eaters, 
Insects, and Cuttle-tishes. Even the Lobster and Crab, in 
addition to their complicated oral organs, have the stom- 
ach furnished with a powerful set of teeth. 
The Sea-urchin is the first of animals, and the only one 
below Articulates and Mollusks, which exhibits any thing 
like a dental ap- . 
paratus. Tive 
calcareous teeth 
having the shape 
of three - sided 
prisms, each set in 
a triangular pyr- 
amid, or “ jaw,” 
are moved upon 
each other by a | 
complex arrange- Fra. 26.—Echinus bisected, showing masticating apparatus. 
ment of levers and muscles. Instead of moving up and 
down, as in Vertebrates, or from right to left, as in Articu- 
lates, they converge toward the centre, and the food passes 
between ten grinding surfaces. 
The minute Rotifers (a group of minute Articulates) 
have a curious pair of horny jaws. That which answers 
to the lower jaw is fixed, and called the “anvil.” The 
upper jaw consists of two pieces called “ hammers,” which 
are sharply notched, and beat upon the “anvil” between 
them. 
The horny-toothed mandibles of Insects, already men- 
tioned, are mainly prehensile, but also serve to divide the 
food in a measure. 
The three little white ridges in the mouth of the Leech 
