INSliCTA. 47-3 



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

 ordinarilj- veiy minute, and scarcely visible. 



Tlio IV'Ijrriapoda 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, whicli 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 insufiicient, 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 metathorux for the hind part of the thorax. f Those oi prothorax 

 and mesoihorax 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 wdiich bears the anterior pair of legs, collar (coUare). 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 comnmn and exposed 

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

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

 (poilriiie), dividing it, according to the segments, into the fore-breast [untipectii.^'], 

 middle breast [medipectiis], and hind breast [po.^tpeciii.'!']. The middle line is the 

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

 sternum [mesostermmi], and hind sternum [metastermim]. 



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 bv 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 



* Ti, iivoid all cotifii.^ioii. it wiialil b.i bt-iter lo restrict tlie term 

 trunk to those .Apterti of Litintciis wliich have more tlo.u six le(,'S, Rod 

 ,vhere tlicse limbs are borne uiioii distinct set,rments, wilb the head 

 distinct from the trunk, lo the Crustacea, where thtise tno parts of 

 the body are soldered together, the thorax might take the name of 

 thoracida, and in the Araehoida, cephalothorax, being: here still more 

 simple, with fewer appendages, that of thorax being reserved for the 



h: ^:ipoli ins, CtS. 



+ This segment ou(;hl not to be restricted, in the Hymenoptera, to 

 the opper, .err short, transverse divisioo of the thorax, at the sides of 

 which the second pair of wings arc ioserted, being further composed 

 of that portion of the lliorax which extends to the base of the abdo- 

 meo as is proved by the position of the two last spiracles of the trunk, 

 1 eve,', Ibiok tilts observalioo is applicable to .11 winged insects, the 



oictatliorax being diviilcii, on the upper jhlc, into two parts, ooe 

 bcariog, io the four-winged speccs, the seeood wi,,gs, and beii,g des- 

 titue of spiracles, and the other being furnished with the latter. This 

 second part appears to be depenilcnt upon the abdomen, as in nearly aU 

 Insects, except the petiolated Hytnenoptera, Rhipiptera, and Diptera. 

 So,netinie8 it is incorporated with the thorax, and closes it posteriorly, 

 as ill these last Insects : heitce I have named this second division of 

 the nietalhoras, the medial segment. Thus, all the segments would 

 have a pair of spiracles, but those of the mesothorax, scarcely distinct, 

 or obsolete, in the Hymenoptera and Diptera, and the two metatho- 

 racic, situated upon the segno-nt which immediately follows that which 

 bears the second wings. The abdomen \,ill thus be composed of nine 

 segoieots, of which the last three compose the organs of generation. 



