134 ON STEUCTURE 



podeum and the abdomen. The perfect insect 

 when it emerges has therefore a head, a thorax of 

 four segments, and an abdomen of seven visible 

 dorsal segments in the male, and of six in the 

 female. The < has six ventral segments exposed, 

 and often the apex of the eighth, which is fre- 

 quently elongate, the seventh being almost 

 always short and hidden ; the eighth dorsal seg- 

 ment can be discovered hidden under the seventh? 

 but it is very rarely exposed. The head (a) bears 

 numerous appendages ; a pair of antennae (a 1 ), 

 usually of thirteen joints in the male and o^ 

 twelve in the female; two compound eyes (a 3 ) 

 composed of many facets; three simple eyes (or 

 ocelli) (a 2 ), which are situated on its vertex ; 

 two mandibles ; two maxttlcv, bearing palpi on 

 each side, of a varying number of joints ; and 

 a labium, or tongue, which also bears at its 

 base two four-jointed palpi (cf. fig. 20). 



The thorax, as we are considering it, consists of 

 four segments the prothorax (6 1 ), which bears the 

 two front legs ; the mesothorax (6 2 ), which bears 

 the intermediate pair of legs and the anterior pair 

 of wings ; and the metathorax (6 3 ), which bears 

 the posterior pair of wings and the hind legs. The 



