ORDERS OF INSECTS. 



171 



the four wings are present, but the condition of these varies in 

 different sections of the order. In one group all the four wings are 

 niemLranous (fig. 114); but in the other the posterior wings and 

 the tips of the anteiior wings alone are membranous. The inner 

 portions of the anterior wings are hardened by chitine (fig. 115), 

 and they are known as " heraelytra " (Gr. hemi, half ; and elutron, 

 a sheath). Amongst the more familiar examples of the Hemiptera 

 are the numerous species of Plant-lice {Aphides), the Field -bugs 

 {Pentatoma, fig. 115), the Boat-fly, the Nepa 

 or Water- scorpion (fig. 116), the Cochineal 

 insects, and the Cicadas. 



The Cochineal insects are of considerable 

 commercial importance, as the dried and 

 powdered bodies of. the female constitute 

 the substance known as Cochineal, from 

 which is obtained the brilliant pigment, car- 

 mine. The male insect is winged, and is 

 smaller than the female, which is wingless. 

 They live upon different species of Cactus 

 {Opuntia), and are mainly imported from 

 Mexico, Algeria, and the Canary Islands. 



Numerous species of Aphides or Plant-lice 

 (fig. 114) are known, and they are among the 

 greatest pests of the gardener and fanner, 

 as they are extraordinarily prolific, and live 

 upon the juices of plants. One of the most 

 curious points about the Plant-lice is that 



they secrete a sweet and sticky fluid, which is expelled from the 

 body by two little tubular filaments placed near the end of the 

 abdomen. Ants are excessively fond of this fluid, and hunt after 

 Aphides in all directions in order to obtain it. 



,S. UG.—Nepa cinerea, tlie 

 " Watev-scorpion," show- 

 ing the semi-membranous 

 anterior wings (" hcme- 

 lytra "). 



Order VI. Orthoptera. 



The mouth in this order is strictly masticatory; there are four 

 wings present, but the anterior pair are smaller than the posterior, 

 and of a different texture. The posterior wings are membranous 

 and are folded lengthwise, like a fan ; the anterior wings are 

 leathery, and constitute cases (elytra) for the posterior wings. This 

 order includes the Crickets {Achetidai), Grasshoppers (Acridiidce), 

 Locusts {Locastidm), Cockroaches {Blattidm, fig. 118), and others. 

 Some of them are formed for running, all the legs being nearly 

 equal in size ; others have the first pair of legs greatly developed, 

 and constituting powerful organs of prehension ; whilst others, such 



