THORAX 



229 



these legs and the names of their podomeres are shown in Fig. 165. 

 The mesothorax and metathorax bear each a pair of wings jointed 

 to the anterior corners of the notum. The wings are membranous 

 folds of the skin, in which the epidermis has practically disappeared 

 and the two layers of cuticle have come together. Branched 

 ridges known as ' veins ' or nervures strengthen the wings. The 

 veins are hollow and each contains a trachea (p. 234) and a nerve. 



Fig. 164. — The mouth-parts of a cockroach. — From Imms. 



I, Mandibles; ab.m., ad.m., abductor and adductor muscles; 2. maxilla; c, cardo; g., galea; /., 

 lacinia ; mx.p., maxillary palp ; s., stipes ; 3, labium ; gl., glossa ; l.p., labial palp ; w., men turn ; 

 pg.,. paraglossa ; pgr., palpiger ; pm., prementum ; sm., submentum ; 4, hypopharynx ; sL, left 

 vestigial superlingua. 



The first pair of wings are dark-coloured and tough (the tegmina) 

 and form a cover for the second, which, when they are at rest, 

 are folded lengthwise and laid along the back. In the female of 

 B. orientalis the wings are very small. \Mngs are not appendages 

 of the same kind as the Umbs, but movable expansions of the terga. 



ABDOMEN 



The abdomen consists of ten somites, each with a tergum and 

 a sternum, joined at the sides by soft cuticle. The hinder somites 

 are telescoped, so that the eighth and ninth are hidden, except 



