HFTMIPTERA. 403 



Here the antennas are composed of from ten to eleven joints, the last of 

 which is terminated by two seta). 



They possess the faculty of leaping, and form the genus 



PSYLLA, Geoffroy. CHERMES, Linnfeus. 



These Hemiptera, also called pseudo-aphides, or faux-pucerons, live on the 

 trees and plants from which they derive their nourishment ; both sexes are 

 furnished with wings. Their larvae usually have a very flat body, broad head, 

 and the abdomen rounded posteriorly. Their legs are terminated by a little 

 membranous vesicle accompanied beneath with two hooks. Four wide and 

 flat pieces, which are the sheaths of the elytra and wings, distinguish the 

 nymph. Several in this state, as well as in the first, are covered with a white 

 substance resembling cotton, arranged in flakes. 



The remaining Aphidii have but six or eight joints in the antennae ; the 

 last is not terminated by two setae. 



Sometimes the elytra and wings are linear, fringed with hairs, and extended 

 horizontally on the body, which is almost cylindrical; the rostrum is very 

 small or but little distinct. The tarsi are terminated by a vesicular joint 

 without hooks. The antennae consist of eight graniform joints. Such are the 

 insects which form the genus 



THRIPS, Linnaus. 



They are extremely agile, and seem to leap rather than fly. When we 

 irritate them beyond a certain point, they turn up the posterior extremity of 

 their body in the manner of the Staphylini. They live on flowers, plants, 

 and under the bark of trees. The largest species scarcely exceed one line in 

 length. 



Sometimes the elytra and wings, oval or triangular, and without a fringe of 

 hairs along the margin, are inclined or tectiform. The rostrum is very 

 distinct. The tarsi are terminated by two hooks, and the antennae have but 

 six or seven joints. Such is the genus 



APHIS, Linn&us. 



In Aphis, properly so called, the antennae are longer than the thorax, and 

 consist of seven joints, the third of which is elongated ; the eyes are entire, 

 and there are two horns or mammillae at the posterior extremity of the 

 abdomen. 



Almost all Aphides live in society on trees and plants, of which they suck 

 the juices with their trunk. The two horns observed at the posterior extremity 

 of the abdomen in a great number of species are hollow tubes from which 

 little globules of a transparent, honey-like fluid frequently exude, on which 

 the ant eagerly feeds. 



The wounds inflicted on the leaves or tender twigs of plants, by Aphides, 

 cause those parts of the vegetable to assume a variety of forms, as may be 



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