304 NATURAL HISTORY OF ARTHROPODS. 



and the greater part of the digestive organs. Spiracles, or breathing pores, open in 

 the flexible membrane which connects the dorsal and ventral pieces of the abdomen. 

 At its extremity, between the dorsal and ventral pieces, open, in a common cleft, 

 the anal and genital orifices, and on each side are often structures of greater or less 

 complicity, generally hidden from outside view, constituting the genitalia or genital 

 armature. The genitalia are often more visible in pupae, as is the case with many 

 pupae of Lucanidae and Scarabaeidae, than in images. 



While the abdomen of adult beetles have no appendages except the genitalia, a few 

 beetle larvas, among which are those of Gyriuidae and Psephenidae, have gill-append- 

 ages borne by several abdominal segments. 



Adult beetles enjoy locomotion of several sorts,' flying, springing, climbing, crawl- 

 ing, or running ; a few add swimming : their larvae sometimes swim, but more com- 

 monly only crawl or run. 



The legs of adult beetles, as well as those of their larvae, are appendages of the 

 three thoracic segments, and are modified according to the' purposes for which they 

 are used. In some larvae one or more pairs of legs are reduced to the merest rudi- 

 ments or entirely disappear, but in the mature beetles no such reduction takes place. 

 The typical constitution of the legs of adult Coleoptera is as follows : the basal joint, 

 short but of various forms, is termed a coxa, and the cavities into which the coxae are 

 set on the under side of the thoracic segments, on each side of the median line, are 

 called coxal cavities. The form of the coxa? is of importance in distinguishing the 

 families of Coleoptera. Jointed to the coxa is a piece named the trochanter; the con- 

 nection of the trochanter with the next following piece the femur is very intimate 

 in some beetles, in others the hind trochanters are prominent lobes upon the inner side 

 of the femora, The femur, or thigh, is the first long piece of each leg ; the tibia, an- 

 other long piece, follows it, and to the latter piece is jointed a foot or tarsus, consist- 

 ing of from three to five short joints, the terminal joint generally having two claws, 

 and between the claws a small appendage, the onychium. The tarsal joints are hairy 

 beneath, and those of the anterior (and sometimes also the middle) pair of legs of 

 many male beetles are modified to clasp more firmly the female during copulation. 

 The most peculiar of these modified tarsi are those of the males of the water-beetles 

 belonging to the family Dytiscidae ; their tarsi will be further described when treating 

 of that family. The form and proportion of beetles' legs are quite varied. Legs 

 fitted for walking and running, ambulatorial and cursorial legs as they are called, are 

 slender, and rather long in proportion to the size of the insect. Fossorial legs, or 

 those intended for digging, are short, stout, and flattened. Springing legs, or salta- 

 torial legs, have generally much thickened femora. Natatorial legs, those used for 

 swimming, are oar-shaped or paddle-shaped, and are bordered with hairs. 



The elytra, which are really horny forward wings, and in which the remnants of 

 veins often can be seen, are generally opened out nearly or quite at right angles to the 

 body in flight, and serve to balance and to steer the beetles, while the two membran- 

 ous wings, which are ordinarily hidden beneath the elytra, unfold, and, by their rapid 

 vibrations, furnish the impulse in flight. Jousset de Bellesme thinks the elytra govern 

 direction in flight by changing their position, and consequently altering the position 

 of the centre of gravity of the beetle. In the Cetonians, a portion of the Scarabaeidae, 

 the elytra are said to remain closed in flight, the wings projecting out from beneath 

 their bases. The inflexed outer margins of the elytra are designated as epipleurae. 

 The venation of the wings of Coleoptera at first glance appears simple, but the devices 



