DESCRIPTION AND CLASSIFICATION OF INSECTS. 35 



buds and leaves of pine trees, &c. Some species are of the 

 utmost importance to the industrial arts, as the silkworm family. 

 Others again greatly destructive, as the larvae of the Cossus Lig- 

 niperda, which burrows in willows, poplars, the ash, and other 

 trees. In another family of this order we find the peach worm, 

 the larva of JEgeria Exitiosa, the palmer worm, the larva of 

 Chcetochilus Pometellus, and a host of others. 



ORDER IX. 

 Diptera. (Dis twice, ptera, wings.) 



55. The distinguishing character of the Diptera is the single 

 pair of wings. The mouth is furnished with a proboscis, and 

 behind the true wings are placed two small organs, called poisers 

 or balancers, (halter es) one on each side. The larvae of these 

 insects are found in every conceivable situation ; some are aqua- 

 tic, others live in and on fungi, in carrion, in flowers, in galls, in 

 meat vats, &c., &c. The perfect insect feeds upon the juices of 

 vegetables, or the blood of animals, or decaying vegetable and 

 animal products, or on other insects. Many of the species are 

 eminently noxious and troublesome ; such are bot flies, grain 

 flies, mosquitoes, and numerous flies which torment and some- 

 times destroy domestic animals. It is sufficient to mention the 

 Hessian fly and the wheat midge to stamp this order with due 

 importance. 



56. The technical characters of the genus (cecidomyia) to 

 which the Hessian fly and wheat midge belong, are as follows : 

 Wings resting horizontally, and having three longitudinal ner- 

 vures ; head hemispherical ; antennae as long as the body, and 

 generally twenty-four jointed, the joints hairy ; (in the females 

 fourteen-jointed ;) the two basal joints short ; legs long ; basal 

 joint of the tarsi very short, second long. 



