HEMIPTERA. 571 



from which they obtain their nourishment ; the two sexes are winged ; the larvje have the body gene- 

 rally very flat ; the head broad, and the abdomen rounded behind. Their legs are terminated by a 

 membranous vesicle, accompanied beneath by two ungues. Four broad pieces, which are the sheaths of 

 the wing-covers and wings, distinguish the pupas : many in this state, as in that of the larva, are 

 covered by a white cottony secretion, arranged in flakes. Their excrements, form threads or masses, of 

 a gummy saccharine nature. 



Some species, by puncturing vesfetables to extract the sap, produce in various parts, especially in the flowers and 

 buds, monstrosities, having the appearance of galls. In this number is Psylla Bii.vi, figured by Reaumur, 

 31em. Ins., vol. iii. pi. 19, fig. 1—14, which is found on the box. The alder, fig, nettle, &c. produce other 

 species. 



LatreiUe has formed with the species which lives in the flowers of Juticus articulatus, a genus, under the name 

 of Livia. The antennae are much thickened at the base. 



[Mr. Curtis has published the figure of another genus under the name of LivHla, founded upon a small, inter- 

 esting British species.] 



The other Aphidii have only six or eight joints in the antenna;, the last of wliich is not terminated 

 by two setae. 



Sometimes the wing-covers and wings are Unear, fringed with hairs, and carried horizontally upon 

 the body, which has nearly a cylindrical form ; the proboscis being small, or scarcely distinct. The tarsi 

 are terminated by a vesicular joint without ungues ; and the antenna? have eight somewhat mouiliform 

 joints. Such is the genus 



Thrips, Linn.,— 

 The species of which are extremely active, and appear to leap rather than fly. When much irritated, 

 they elevate and bend the extremity of their bodies into an arch in the same manner as the Staphylini. 

 They live upon flowers and plants, and under the hark of trees. The largest species scarcely exceed a 

 line in length. 



LatreiUe observes in a note that the structure of the mouth exhibited to him characters 

 which appeared essentially to distinguish the species of Thrips from the other insects of 

 this order. M. Strauss also, who had studied them with admirable precision, considered 

 that they belonged to the order Orthoptera. [Subsequently, the genus has been raised 

 to the rank of a distinct order by Mr. Haliday in a valuable memoir published in the En- 

 tomological Magazine, imder the name of Thysanoptera, and I have illustrated the structure 

 of the mouth in my Modem Classification of Insects, vol. ii. p. 1, with figures. Mr. 

 F. iu2.--Thrips. jjaliday has established a number of generic and subgeneric divisions.] 



Sometimes the wing-covers and wings are oval or triangular, without a fringe of hairs, and are 

 deflexed at the sides like a roof ; the rostrum is very distinct ; the tarsi are terminated by two ungues ; 

 and the antennae have only six or seven joints : these form the genus 



Aphis, Linn. 



Aphis, proper, has the antennae longer than the thorax, 7-jointed, the third being elongated; the eyes are entire, 

 and the posterior extremity of the abdomen is furnished with two horns or tubercles. 



They live mostly in society upon trees and plants, which they suck with their proboscis. They do not leap, and 

 crawl but slowly. The two horns at the extremity of the body in many species are 

 tubes, from which frequently exude small drops of a transparent saccharine fluid, 

 [termed honey-dew], of which the ants are very fond. Each society consists in spring 



and summer of plant-lice always apterous, and of pupae [demi-nymphes], of which the -- »^ , , ~V \*« 



wings ought to be developed ; all these individuals are females, which produce living V ^^ 



young, which are ejected tail foremost, without any previous coupling. The males, ^'S- los.— .■\phis Rus». 



amongst which some are winged and some wingless, appear only at the end of the summer or in autumn. They 

 fecundate the last generation produced from the preceding indiriduals, consisting of wingless females which 

 require impregnation, after which they deposit eggs upon the branches of trees, which remain in that state all 

 through the winter, from which young plant-lice are produced in the spring, capable of multiplying without union 

 with the males. 



The influence of a single impregnation thus extends through several successive generations. Bonnet, to whonj 

 we are indebted for the majority of the facts observed upon this subject, obtained, by the isolation of females, 

 nine generations in the space of three months. The punctures which the plant-lice make in the leaves and young 

 twigs of vegetables, often cause these parts to assume different forms, as may be seen in the young buds of the 

 lime, the leaves of the gooseberry, pear, and especially of the elm, poplar, &c., where they produce a kind of vesi- 

 cles or excrescences, containing whole families of plant-lice, and often a saccharine fluid, in the interior. The 



