INSECTA. 



47o 



the canal of the nutritive fluids. At the base of each of these filaments there is a palpus 

 ordinarily very minute, and scarcely visible. 



The Myriapoda are the only species of which the mouth exhibits another type of con- 

 struction, which I shall describe when treating upon those insects. 



The trunk* of insects, or that intermediate portion which bears the feet, is generally 

 designated by the Latin name thorax, which the French term corselet. It is formed of 

 three segments, which were not at the first carefully distinguished, and of which the 

 relative proportions greatly vary. Sometimes, as in the Coleoptera, the anterior is by 

 far the largest, separated from the following by an articulation, moveable, and alone 

 exposed ; which alone appears, at first sight, to compose the trunk, and bears the name 

 of the thorax, or corselet. Sometimes, as in the Hymenoptera, Lepidoptera, &c, it is 

 much shorter than the following, and constitutes, with the two others, a common 

 body, attached to the abdomen by a peduncle, or closely united to it throughout its 

 entire posterior breadth, and which is called the thorax. 



These distinctions, thus established, were insufficient, and often ambiguous, as they 

 did not rest upon a ternary structure of the thorax, as I had clearly noticed in the first 

 edition of this work, as a character proper to hexapod insects. Mr. Kirby has em- 

 ployed the name of metathorax for the hind part of the thorax. f Those of prothorax 

 and mesothorax naturally presented themselves to the mind when the ternary division 

 of the thorax was once adopted, and the celebrated Professor Nitzsch was the first who 

 used them. Some naturalists have since named the prothorax, or anterior thoracic 

 segment which bears the anterior pair of legs, collar (collare). Wishing to preserve 

 the name corselet, but to restrain its application in proper limits, we shall employ it in 

 all those cases where this segment greatly surpasses the others in size, and where the 

 latter are united to the abdomen so as to appear to constitute an integral part of it, — 

 a peculiarity proper to the Coleoptera, Orthoptera, and many Hemiptera. When the 

 prothorax is short, and forms, with the succeeding segments, a common and exposed 

 mass, the trunk, composed of the three segments together, will retain the denomination 

 of thorax. We shall also continue to call the inferior surface of the trunk the breast 

 (poitrine), dividing it, according to the segments, into the fore-breast [antipectus], 

 middle breast [medipectus] , and hind breast [postpectus] . The middle line is the 

 sternum, which we also divide into three: — The fore sternum [prosternuni], middle 

 sternum [mesosternurn], and hind sternum [metasternuni] . 



The teguments of the thoracic segments, as also those of the abdomen, are generally 

 divided into rings or semi-rings : one dorsal, or superior, the other inferior, and united 

 laterally by means of a soft and flexible membrane, which is indeed but a less solid 

 portion of the same teguments in many insects, especially the Coleoptera. We also 

 observe, at the reunion of these rings, a small space, more solid, or of the substance of 



• To avoid all confusion, it would be better to restrict the ti*rin 

 trunk to IhoM Aptera of Untunila which have mure thin MX Ic^n, and 

 where those limbs srobornc opon distinct segments, with the head 

 distinct from the trunk. In the Cmstmces, where these two partsof 



.y art- soldered together, thr thorax might tain- the name of 



thoracida, and in the Ami tinlda, cephnlothoru, being here itUl more 

 B, with fewer appendagci, that of thorax being reicrvcd for the 

 t. p id him cts. 



+ This segment onghl not to be restrleted, In the Hymenoptera, to 

 the upper, eerj short, tmnsvi rse division ol lbs thorax, at the 



which the 11 I ""'k' 1 sis Inserted, a further composed 



of that portion of the thoru which extends to the h«%e nf the abdu- 

 men, ss Is Iwt spiracles ol the trunk 



1 even think this obsemtl in i» upplicsblc to all winged IniccH, the 



metathorax being divided, on the npper m<!<\ Into two psrts, one 

 bearing, in the four-winged species, the second wings, aiol brio,; det- 

 t spiracle*, and 1 lie other being furnlshi ii with tin Intter. rhls 

 perl appenrs to be dependent upon the nbdomen, an in ns 



11 tcra, and DlpterSw 



rpoi ''■ d with ilo- thor ix, end I ""rly, 



M In these last Insects 1 hence] bats named thii 

 the metathorax, the medial >■ 1 nentiwould 



. p lit of --I'lri' les, bnt those of the 1 

 or obsolete, In the Hrmeno] . 1, and the two metatho* 



r ii.. ittnated upon tin- segment a hlch Immedl itt iv follows that *» hick 

 ngs. The sbdomen will thu, be composed of nine 

 Dts, of which the last three cm. fnaaratioo* 



