INSECTS. 



[ 358 ] 



INSECTS. 



compressed, and frequently furnished with 

 spines, spurs or other appendages, especially 

 at its end ; in the ant the tibiae have each a 

 beautiful pectinate process. The last portion 

 is the foot or tarsus (fig.365p; PI. 27. 6, 7 ), 

 which consists of several joints arranged in 

 a row. The number of these joints varies in 

 different insects; sometimes it is different 

 in the anterior and posterior pairs of legs ; 

 they are, however, most commonly five. 

 The last joint of the tarsus is usually fur- 

 nished with appendages, in the form of 

 hooks or claws, mostly two, and frequently 

 serrated, especially near the base. Some- 

 times also it has two or three delicate mem- 

 branous or fleshy cushions, called pulvilli 

 (PL 27. figs. 7 & 8) ; these are more or less 

 covered with hairs, which are sometimes 

 terminated by little disks (fig. 9), and by 

 which it is supposed that the insects are 

 enabled to ascend or adhere to polished 

 surfaces in opposition to gravity. In other 

 insects elegant brush-like appendages are 

 met with in the same situation. Disks of 

 the same kind but larger, and peculiarly - 

 arranged hairs, sometimes occur upon the 

 upper joints of the tarsus (PI. 27. fig. 6, DY- 

 TISCUS ; and fig. 4 a, APIS). 



The structure of the legs of insects in the 

 larval state (PI. 27. figs. 32, 33) differs con- 

 siderably from that of the imago as de- 

 scribed above. 



The wings are dry, membranous, and 

 transparent organs, consisting of two 

 laminae or plates, which are confluent at the 

 margins ; these plates may be regarded as 

 folds of the integument. Between them 

 run canals, commonly called veins, nerves or 

 nervures, which are more or less numerous 

 and ramified ; and upon their arrangement, 

 the distinguishing characters of the genera, 

 &c. are sometimes founded ( WINGS). The 

 veins are formed by two wide horny half- 

 canals in the upper and under plates, of 

 which the wings consist. The main veins 

 arise from the point of attachment of the 

 wings to the thorax, and gradually diminish 

 in diameter until they reach the extremity 

 of the wings. The veins convey the circula- 

 ting liquid, and contain each a tracheal 

 branch, which communicates with the tracheae 

 of the thorax. In flight they are said to be 

 distended, and the wings kept expanded by 

 air from the interior of the body. In some 

 kinds of wings the circulating currents are 

 not confined to narrow channels as in the 

 veins, but traverse a large part of the breadth 

 of the wings (COCCINELLA). 



Most insects have four wings; but in 

 some, the males only are furnished with these 

 appendages. In the Diptera, the posterior 

 pair of wings are rudimentary, being replaced 

 by two little club-shaped bodies, called the 

 halteres, poisers, or balancers. In this order 

 also, and in some insects belonging to other 

 orders, a pair of small and rounded membra- 

 nous or scaly appendages are attached to 

 the back of the base of the first pair of 

 wings, called in the former the squamae 

 halterum, and in others, alulae or winglets. 

 The anterior pair of wings are in some 

 insects, as in the beetles, Coleoptera, hard, 

 horny and opake, forming wing-covers or 

 ELYTRA (fig. 371), and the lower wings, 

 which are usually larger, are folded together 

 beneath them, when at rest. In others, the 

 posterior wings disappear, and the elytra 

 coalesce at their inner margins. Sometimes 

 the anterior wings are horny or leathery at 

 the base, and membranous towards the 

 summit (fig. 370); these are called hemelytra. 

 At others, all the wings are thin, membra- 

 nous, and transparent, as in the Hymenoptera 

 and Neuroptera. 



In the Lepidoptera, they are covered with 

 beautiful feathers or SCALES. In this order 

 also, there exists upon the upper side of the 

 prothorax, a pair of oval plates covered with 

 hairs, and called patagia or tippets. The 

 mesothorax also is furnished at its sides with 

 a pair of large triangular scales, called pte- 

 rygodes, paraptera, or tegulae; these are 

 attached to the upper part of the base of the 

 anterior wings, and they are often covered 

 with hairs or scales of a different colour 

 from those on the other parts of the thorax. 



There exist also other modifications of 

 the wings of certain insects, adapting them 

 for special functions. In the Orthoptera 

 these modifications are the agents producing 

 the well-known chirping sounds, as in the 

 male cricket and grasshopper. In the common 

 house-cricket, Acheta domestica, each of the 

 upper wings or elytra exhibits a clear space 

 near the centre (PL 27. fig. 10 a), traversed 

 by a single vein only, or at least by a very 

 few veins. This space has received the name 

 of the drum or tympanum. Bounding it ex- 

 ternally is a large dark longitudinal vein, 

 provided with three or four elevated longi- 

 tudinal ridges. Immediately in front of the 

 tympanum, near the base of the elytra, is a 

 transverse horny ridge, tapering outwards 

 and furnished with numerous short trans- 

 verse ridges or teeth, and forming a kind of 

 file or bow (PL 27. fig. 106). When the 



