40S ARTHROrODA 



(fig. 447) is a long tube coiled like a \yatcli spring licncalh ihc Iicad. It con- 

 sists of two long grooved maxillary galea firmly united by their edges. The 

 maxillary palpi are well de\eloped in the moths; elsewhere they show all stages 

 of reduction to complete disappearance. Labium and labrum are reduced to 

 small triangular plates at the base of the proboscis, the laliium bearing a pair of 

 hairv palpi (pi). The mandibles are represented, by small plates or bunches of 

 hair. These conditions gain in interest when we remember that in the larva 

 the mandibles are strong biting organs, while the maxilla; are small hooks, and 

 the labium is better developed only in those parts connected with the silk glands, 

 a beautiful example of relations of structure to life conditions. 



In contrast to the other regions, the abdomen lacks ap]iendages in the adults. 

 Only in the Thysanura are small lobes present, behind and in the same line with 

 the thoracic feet, which may be abdominal feet. A])parentlv, too, the append- 

 ages of the last segment, the slyhi.^ and ccn'i, are modified limbs, but the parts 

 {i;oiiapoplivscs) used in copulation and o\iposilion are dift'erent in character. 

 False feet, or pro-legs, occur on the abdomen of the larva; of the Lepidoptera and 

 the Tenthredinida:, but since these are fleshy unjointed processes, it is doubtful 

 whether these are true abdominal limbs, or are structures independently 

 acc|uired. 



Besides ventral appendages the insects usually have two pairs of dorsal 

 outgrowths upon the meso- and metathorax, the wiitgs. They are lateral 

 folds of the chitinous coat of the notum and contain on their interior exten- 

 sions of the blood sinuses and of the tracheal which are protected by tltick- 

 enings of the chitin, causing the network of 'veins' or 'nervures' In the wing. 

 Both wings may be elastic, llexible, and adapted for flight, or the liinder 

 pair may aloiie partake of tliis character (true wings or ahc). wliile the 

 first pair may be tliick and parchnient-like wing covers, or elytra, under 

 which the true wings are concealed wiien at rest. \\'hen onh- the base of 

 the wing is thus tliickened licmclytni result. Between the bases of the 

 anterior wings is fre(iuently a cliitinous plate, the sciilcUinu, between the 

 liinder wings a similar postsculcUiim. In many insects one pair of wings 

 is lacking, the anterior pair being retained in the Diptera (fig. 486), the 

 posterior in the Strepsiptcra (fig. 469). The entire absence of wings may 

 occur from two causes; wings ha\e apparently never been developeil in 

 some (primary lack of wings of the Apterygota), witile there are others in 

 which wings once present have been lost, because nearly relateil forms 

 ■ — bugs, male cockroaches, sexual ants and termites — arc winged (figs. 

 464, 482, 4S3). The prothorax of all recent insects is wingless, but some 

 Archiptera of the coal period had wing rudiments on this somite. 



As a result of dilTercnces in food the alimentary canal (figs. 448, 440) 

 varies greatly. The ectodermal stomodxunt begins with a pharynx, which 

 in the sucking insects is a sucking ap])aratus with radial muscles. The 

 cesophagus, which follows, may he widened to a crop (ing,luvics), or it may 

 ha\-e a oucal outgrowth wiiich in the butterfiics and Hies may take the 

 shape of a stalked \-esicle (falsely 'sucldng stomach'). Also ectodermal 



