INSECTS : THEIE MOUTHS. 161 



or sinkings of the surface, along its front edge. This is 

 the upper lip ; but, instead of being fleshy, as ours is, 

 it is composed of a hard polished black shelly substance, 

 of a peculiar nature, called chitine, the same substance 

 as the hard parts of all Insects and Cnistacea are 

 made of. 



From beneath the sides of this there project on each 

 side two broad hooked pieces, which, as you see, I can 

 Avith a needle force out laterally, so as to show their 

 form better, for they hinge upon the sides of the face, 

 beneath the heads-hield. Each forms the half of a cres- 

 cent, the curved points of which are turned towards 

 each other, and can work upon each other, the points 

 crossing, like shears. These are tEe proper biting jaws, 

 or mandibles, and in many of the larger beetles they 

 have great power of holding and crushing. Some- 

 times, their inner side is cut into strong teeth, but here 

 this side forms a blunt cutting edge ; the upper surface, 

 however, is scored with ridges and furrows, like a file, 

 and this structure is best seen in the left jaw, which, 

 when the pair close, crosses over the right. This is an 

 action of the jaws the reverse of ours, but it is char- 

 acteristic of all the articulate classes of animals, in 

 which the jaws, whenever present, always work hori- 

 zontally, from right to left, and not vertically, up and 

 dovsm. 



I will now, by making the forceps revolve, bring 

 the -under side of the head into view ; for without sep- 

 arating the parts by dissection (which, however, is by 

 no means difficult,) it is impossible to see them all from 

 one point of view. The part nearest our eye now is 

 the chin, a wide homy piece, like the upper lip, jointed 

 to the head by its straight hind edge, but, unlike it. 



