T&E ORDERS OF INSECTS. 5 



comb, or of the feather of a bird. Sometimes they are tapering 

 at the end ; sometimes knobbed ; and sometimes, again, they 

 have a series of long processes near the end, opening and closing 

 at pleasure, almost like a fan. 



The mouth of insects is formed either for biting or for suction. 

 Those which have horny jaws are called mandibulate insects 

 {Insecta Mandibulata), and those which are provided with a pro- 

 boscis to imbibe liquid food are called haustellate insects (Insecta 

 Hanstellata). Most of the latter, however, are mandibulate in the 

 larva state, and many mandibulate insects are likewise provided 

 with a proboscis. 



The three segments of the thorax are called the prothorax, 

 mesothorax, and metathorax respectively. The first bears on the 

 under surface the first pair of legs. The second bears the first 

 pair of wings, and the second pair of legs ; and the third bears 

 the second pair of wings, and the third pair of legs. The 

 under surface of the thorax is called the pectus, and the space 

 beneath the wings the pleura. The two pairs of wings are not 

 always alike, and when there is any difference, the first pair are 

 always thicker and narrower. When they are much harder and 

 thicker than the hind wings, so as to form wing-cases rather 

 than additional organs of flight, they are called elytra. The 

 wings are always traversed by a greater or less number of jointed 

 air-tubes, called nervures, the arrangement of which differs con- 

 siderably in various insects. The legs are divided into several 

 parts. First come the coxce, or hips, which are generally the 

 thickest parts of the leg ; next a connecting joint, called the 

 trochanter ; after which follow two straight parts, called femora, 

 or thighs, and tibiae, or shanks, respectively. Below these comes 

 the foot, which is composed of five joints, called joints of the 

 tarsi, and terminating in a pair of claws ; but in many insects, 

 the claws, or even one or more of the joints of the tarsi them- 

 selves, are undeveloped. The point of intersection of the femur 

 and tibia is called the knee ; and the knees, like the trochanters, 

 are occasionally of a different colour to the rest of the leg. The 

 legs, like the rest of the body, may be smooth, or clothed with 

 hairs, or spines ; there are often a pair of long spurs at the end 

 of the tibiae, and sometimes also in the middle. 



In many insects, the abdomen is completely covered by the 

 wings when the insect is at rest ; while in other cases, it projects 

 far beyond them. Its latter extremity is often furnished with 

 a variety of curious appendages, which are either directly or 

 indirectly defensive or offensive weapons, or connected with the 

 reproduction of the species, and oviposition. 



