HOW ANIMALS EAT. 



227 



members of the spider and centiped classes which eat solid matter 

 have masticating jaws. But the best development of such jaws is 

 found in the insects. Nearly all insects while in the larval state, and 

 many adult insects, as beetles and grasshoppers, have two pairs of 



::7f- : 



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I: I 





Fig. 4. Pig. 5. 



Lower Jaws of Ancient Toothed Birds (after Marsh). 



Fig. 4 : Ichthyornis dispar. Twice the natural size. Teeth in distinct sockets. Fig. 5 : Eesperor- 



nis regalis. One half natural size. Teeth set in a groove. 



jaws, called mandibles and maxillae, which move horizontally between 

 upper and under lips. Such insects usually have gizzards to complete 

 the mechanical process. The grasshoppers and others have the giz- 

 zard armed with rows of horny teeth. The activity and efficiency of 



