102 THE FOOD OF ANIMALS 



(i) the head, provided with feelers (antennae), eyes, and other 

 sense organs, and bearing three pairs of limbs specialized as jaws ; 

 (2) the thorax, carrying three pairs of legs and two pairs of wings; 

 and (3) the abdomen, devoid of obvious limbs, though modified 

 traces of these are usually present at the hinder end. For our 

 present purpose the jaws merit special attention. They are known 

 as mandibles, first maxillae, and second maxillae, when taken in 

 order from front to back, and are clustered together in the neigh- 

 bourhood of the mouth-opening, the first pair of them being 

 overlapped by the second, and these again by the third. In the 

 Cockroach they are in a comparatively simple condition: the 

 mandibles are strong, horny jaws adapted for biting; the first 

 maxillae are also provided with cutting pieces; and the second 

 maxillae are partly fused into a sort of plate which acts as an 

 under lip, or labium as it is often called. Jointed feelers or 

 palps are borne by both pairs of maxillae, and are termed 

 respectively maxillary palps and labial palps. It should further 

 be remarked that a broad upper lip or labrum overhangs the 

 mouth in front, and the mandibles and first maxillae work from 

 side to side in the space between upper and lower lips, effectively 

 biting anything that may happen to be between them. An 

 insect with jaws of the sort just described is said to have 

 biting mouth-parts; but in other cases the corresponding parts 

 may be specialized into sucking, licking, or piercing organs, as 

 will be shown in the sequel. Indeed, the mouth-parts of insects 

 afford one of the best -known illustrations of modifications for 

 special purposes based on a common type or plan of structure, a 

 principle which frequently recurs in the animal kingdom. 



The nine orders of Insects may roughly be divided into two 

 sets, according as the mouth-parts are suited for biting or modified 

 into suctorial structures. 



A. — Insects with biting mouth-parts (in the adult). 



1. Membrane-winged Insects (Hymenoptera).— Bees, Wasps, 

 Ants, &c. 



2. Beetles (Coleoptera). 



3. Net-winged Insects (Neuroptera).— Dragon-Flies, Termites, 

 May-Flies, &c. 



4. Straight- WINGED Insects (Orthoptera). — Cockroaches, Crickets, 

 Locusts, Grasshoppers, Earwigs. 



5. Wingless Insects (Aptera).— Primitive forms, in some of which 

 the mouth may be imperfectly suctorial. 



