16 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



conspicuous compound eyes. These eyes are called compound 

 because they are made up of a great number of small eyes lying 

 very close together. Examined with a hand lens or the low 

 power of a microscope the compound eyes show a honeycomb- 

 like structure, each of the small hexagonal facets being the 

 external surface of a simple eye. In slight depressions just in 

 front of the eyes are the bases of the long, many-segmented 

 antenna. These antennae are sense organs and are used by 

 the locust for feeling and perhaps also for smelling. In many 

 other insects they are modified and plainly used for smelling 

 and also, in some, for hearing. In the middle of the front of 

 the head, a little lower than the bases of the antenna?, is a small 

 transparent hemispherical simple eye or ocellus. Just above 

 the bases of the antennas and close to the compound eyes are 

 two other simple eyes. The structure and function of these 

 three ocelli as well as the structure of the compound eye is 

 discussed in Chapter XVI. On the lower side of the head are 

 the mouth-parts. The upper, broad, flap-like piece, the 

 labrum, covers a pair of black or brown, strongly chitinized, 

 toothed jaws, or mandibles. Back of the mandibles is a second 

 pair of jaw-like structures, the maxilla, each of which is 

 composed of several parts, and back of the maxillae is the labium 

 which is also composed of several pieces. Each maxilla 

 bears a slender feeler, or palpus, composed of five segments. 

 The labium bears a pair of similar palpi, which are, however, 

 only three-segmented. The mandibles and maxillae, which are 

 the insect's jaws, move laterally, not vertically, as with most 

 animals. They are well adapted for tearing and crushing the 

 leaves or other plant tissue upon which the locust feeds. Some 

 other kinds of insects will be found to have these mouth-parts 

 curiously modified, enabling them to pierce the animal or 

 vegetable tissues on which they are feeding or to lap up or 

 suck up liquid substances. 



The Thorax. The thorax is composed of three segments 

 which can be easily recognized by the appendages which they 

 bear. The first segment, the prothorax, is freely movable and 

 is covered by a large hood-shaped piece, the pronotum, which 

 also extends back over the next segment. The first pair of 



