Page:Popular Science Monthly Volume 17.djvu/239

Rh 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



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