207 



The head varies endlessly in size and shape, and the mouth-parts 

 are correspondingly diversified. In some orders they consist of man- 

 dibles and maxillae, which work transversely between the labrum and 

 labium, and there are also attachments known as maxillary and labial- 

 palpi. Several of these parts are again subdivided, and in all there are 

 nearly a score of parts, each with its distinguishing name, to be studied 

 in connection with the mouth alone. Then there occur many modi- 

 fications of these organs, in which certairt parts are so altered that the 

 entire form of the mouth is changed. Then the lepidoptera, diptera 

 and hemiptera have the mouth-parts transformed into a rostrum or 

 proboscis which serves to suck the nectar from flowers, or the vital 

 juices from plants and animals. The head also bears the eyes, which 

 consist generally of two large aggregations of facets, often to the number 

 of several thousands, besides which the majority of insects have two or 

 three simple eyes, or occelli. The antennse, also placed upon the head 

 are movable sense organs which perform very important functions, 

 and which vary in form. They are composed of small rings or segments 

 the number of which varies in the different groups, and averages perhaps 

 ten or twelve. In the simpler forms of antennce these joints are merely 

 short cylinders placed end to end, but in numerous families one or 

 more of these joints may be enlarged or modified so much, that the 

 antenna becomes very different in appearance, and many terms are 

 employed to indicate the modifications, such as serrate, flabellate, pec- 

 tinate, clavate, lamellate, etc. 



The thorax is formed of a number of plates, more or less solidified 

 and united, and bears the organs of locomotion, usually three pairs oj 

 legs and two pairs of wings. The legs consist of several segments, 

 ending usually in a pair of small claws, and may be variously armed or 

 ornamented with spines and hairs. The wings are formed of two thin 

 transparent membranes stiffened by an interposed net work, more or 

 less complicated, of nervures or veins, and upon this venation of the 

 wings is based the classification of many groups. In beetles one pair 

 of wings is modified and hardened to form protecting sheaths for the 

 hinder pair, and a somewhat similar, but partial, thickening is observed 

 in grasshoppers and bugs. Butterflies and moths have the wings great 

 ly developed and covered with scales and pubescence, which are so 



