INSECTA 



475 



the phloem cells of the plant are eventually pierced and their contents 

 sucked out. The pumping action is performed by the muscles of the 

 pharynx. 



This order comprises a large number of families which in the 

 following scheme of classification are arranged in two suborders, the 

 Heteroptera and the Homoptera. The Heteroptera have wings which 

 are horny distally, but membranous apically (Fig. 331). The pro- 



Fig. 328. Mouth parts of the Hemiptera. A, Sagittal section through head 

 of Graphosoma italiciim. After Weber. B and C, Diagrams of mouth parts 

 and adjacent region of the head. C is a transverse section across B at the 



point X X. After Imms. Ibyn. labium; Ibr. labrum; nid. mandible; 



mx. maxilla; ph. pharynx; ph.p. muscles of pharyngeal pump; sty. stylets. 



boscis is terminal and free. In the Homoptera the fore wings have a 

 homogeneous texture and are ^often membranous. The head is 

 ventrally flexed so as to bring the base of the proboscis into contact 

 with the anterior coxae (Fig. 329). 



There are two tribes of insects within the Heteroptera, {a) those 

 which are aquatic and whose antennae are obscure, the Cryptocerata^ 

 and {b) mostly terrestrial forms with conspicuous antennae, the Gym- 



