INSECTS : THEIR MOUTHS. 139 



nature, called chitine, the same substance as the hard 

 parts of all Insects and Crustacea are made of. 



From beneath the sides of this there project on each 

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

 with a needle force out laterally, so as to show their form 

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

 the head-shield. Each forms the half of a crescent, the 

 curved points of which are turned towards each other, and 

 can work upon each other, the points crossing like shears. 

 These are the proper biting jaws, or mandibles, and in 

 many of the larger beetles they have great power of hold- 

 ing and crushing. Sometimes 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 characteristic of all articulate animals, in which 

 the jaws, whenever present, always work horizontally^ 

 from right to left, and not vertically, up and down. 



I will now, by making the forceps revolve, bring the 

 under side of the head into view ; for, without separating 

 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 

 horny piece, like the upper lip, jointed to the head by its 

 straight hind edge, but, unlike it, having its front edge 

 hollowed out with two deep notches, the central piece 

 between them itself notched at its tip. Immediately above 

 this notched central tooth (I speak of the relative position 

 of the parts, supposing the insect to be crawling on the 

 ground, without reference to the way in which we turn it 

 about on the microscope), and united with it, there is a 

 sort of solid square pedestal, on which stand a pair of 

 jointed organs, and between them an oblong horny plate 

 rounded at the tip, where it bears two bristles. This 



