206 NATURAL HISTORY OF ARTHROPODS. 



in Diptera and dragon-flies. Strongly in contrast to all these we find in the principal 

 Homoptera a head either transverse or vertical, deep-seated, immobile, and prolonged 

 downwards and backwards. In such exceptional groups as the Fulgoridae, the front of 

 the head is either di-awn out into a large inflated protuberance, is curved forwards in a 

 long, tapering horn, or it is shaped like an Indian war club. Two, or at most three, 

 ocelli are generally present, but they are absent in certain groups, such as Pyrrhocoris, 

 Largiis, and Capsiis. 



The thorax constitutes a large portion of the mass of the body, and its first princi- 

 pal di\ision is generally free, as in the Coleoptera. All three sections of this part of 

 the body, the prothorax, the mesothorax, and the metathorax are well distinguished, 

 and are only fused together iu such low forms as Aleurodes, Aphidae, Coccidae, and 

 the lice. 



To these three jjieces the legs are attached, not far out on the sides as in Orthoj)tera 

 and Pseudoneuroptera, but beneath, and generally near the middle line. They are 

 fitted for running, jumping, grasping, or swimming ; and are often provided with 

 curious balancing plates, curved thorns, waved lamellas, or rows of spines. The coxae 

 are also built upon two principal patterns ; the one being more or less conical and 

 rotatory, the other more elongated, fixed, and only capable of motion in the direction 

 of the longitudinal axis of the body. The tarsi have generally three or two joints, 

 rarely only one. Generally there are four wings present, but the posterior ■paiv does 

 not appear in the males of the Coccidfe. The hemelytra and lower wings are devel- 

 oped from the sides of the meso- and metathorax ; and in the Homoptera they are com- 

 monly attached lower down than in the Heteroptera. 



A system of tracheal vessels conveys air to all parts of the body, and communicates 

 with the outer surface by means of openings called stigmata. These openings are 

 provided with a lid or contractile fold, which can be tightly closed to prevent suffoca- 

 tion. In a few of the aquatic forms, Jielostoma, Zaitha, etc., they are apparently 

 closed, but in reality have slit-like or valvular orifices which serve to strain the air and 

 perhaps to admit only the oxygen that it contains. An air-chamber generally rests 

 beneath each of the stigmata, and is connected with the others by tracheal tubes run- 

 ning throughout the length of the body on both sides. The stigmata amount in all to 

 ten on each side ; a pair is placed on the underside of each of the three divisions of the 

 thorax, generally on or near the transverse sutures; six pairs are set beneath on the 

 sides of the abdomen, and a pair is placed above next to the suture which separates 

 the thorax from the abdomen. In Fulgora and its near allies these latter are very 

 large, but are covered by a whitish fibrous secretion in the living insect. In the higher 

 Heteroptera the abdominal orifices are capped by a little prominence resembling a 

 bead, while in Notonecta, Corixa, and some Cicadas they are concealed by fur, hairy 

 filaments, or scales. Ranatra and Nepa possess the usual number of stigmata, but 

 have in extension a pair of long respiratory tubes at the end of the body through 

 which they appear to receive most of the air required. 



A variety of fluids and other substances are secreted by the Hemiptera. Some of 

 these are for the protection of the body or the eggs, as in the Coccidae ; others, perhaps, 

 for defence, as the annoying spray emitted by most of the Heteroptera. In many of 

 the latter a most offensive bug-odor is characteristic of the fluid secreted by glands 

 situated generally in each side of the body behind the mesosternum. Each of these 

 glands communicates exteriorly with an orifice placed behind or near the middle coxa, 

 called the osteole, which generally issues in some kind of an open channel styled the 



