852 



INSECT. 



take the organs of the month seriatim, according to 

 their position, commencing with that which lies 

 uppermost, or, 



The Labrum or upper lip (I I in the figures). This 

 organ is, in biting insects, a horny or leathery flattened 

 plate of variable form, attached, by an articulation, to 

 the clypeus, and serving as an upper covering to the 



92 

 i 



Tig*. 91, Labrum of Mexacrphnlrt g 1 ?, ditto of Aploa ; 93, Perl- 

 liun/iux , 94, Bancitus. 



rest of the mouth ; unlike the lower lip, this organ is 

 never furnished with palpi. In many insects, however, 

 it is quite membranous, and is in such cases completely 

 concealed by the clypeus, with which, indeed, it was 

 sometimes confounded by Fabricius, who also gave 

 to it the name of that part. It is generally fringed 

 with hairs. In some few Humenoptera it is furnished 

 with a slender appendage, to which indeed Illiger 

 applied the name ^labrum. In the Hemiptera the 

 uper lip is in the form of an elongate triangle, which 

 falls upon the base of the canal of the lower lip. In 

 the Lcpidoptcra it is so minute as not to be discerni- 

 ble without great care, appearing as a small triangular 

 piece extending downwards towards the base of the 

 labial palpi. In the Diptera it is either obsolete, or 

 exists in the shape of a corneous slender guiter, hol- 

 lowed beneath, and receiving the other slender lancet- 

 like organs. 



The Mandibles, or upper jaws (w in the figures). 

 These organs, in the generality of biting insects, are 

 the chief instruments by which the food is bitten into 



they are commonly furnished. In some of the lamel- 

 licorn beetles, the internal base of these organs is 

 dilated into a broad ami flattened square plate, having 

 numerous transverse ridges, serving for the purpose 

 of bruising the leaves upon which these insects feed 

 (fig. 97). In some beetles also, which subsist upon the 

 juices of flowers, or upon the flowing sap of wounded 

 trees, &c., the jaws are of a membranous structure, and 

 quite unfitted for mastication. In the Hymcnoptera 

 also.the jaws, although of the ordinary form, cannot, in 

 many cases, be regarded as masticating organs, but 

 appear solely to be employed either in the construe- 

 ; tion or the provisioning of the nest. In the Lepido- 

 I ptcm fchey are very minute, membranous, and trian- 

 ; gular, and placed on each side of the labrum. In 

 i the Hemiptera they are very long, slender, and em- 

 ployed in conjunction with the maxillaB as lancets. 

 I They have also the same character in the Diptera ; 

 i but here they are often entirely wanting. They are, 

 I however, particularly distinct in the gnats and gadflies 

 (Tabanidce) fig. 88, m. 



The Maxill<E, or lower jaws (m x in the figures). 

 These organs are tw o in number.and are placed beneath 



Kigs.95, Mandibles of The rates; pfi, ditto of Hybuma; 97 ditto 

 JUimela; ys, ditto Gueriuu. 



pieces. They have been considered analogous to the 

 jaws of the higher animals, but they have a much greater 

 resemblance to a pair of large and robust, horny, and 

 notched teeth. They are inserted at the sides of the 

 oral aperture immediately below the lower lip, to 

 which, indeed, they appear to bear the same kind of 

 relation as the lower jaws do to the lower lip. They 

 are composed of a single piece, and are destitute of 

 any appendage. In some of the Erachclytra (espe- 

 cially the species ordinarily termed the devil's coach 

 horse, fig. 9<) their inner surface is, however, furnished 

 with a small moveable exarticulate process, as is also 

 the case in Pussalux and Hydrous. By Linnzeus they 

 were termed maxillte. In beetles these organs are gene- 

 rally of large size, and of a horny substance. The 

 large and powerful instruments with which the head 

 of the stag-beetle is armed are the mandibles im- 

 mensely developed; but these organs, like many 

 others, exhibit great variations according to the sexes. 

 In the last-named insect for instance, the jaws of the 

 females are so short that this sex was long regarded 

 as a distinct species. They are usually symmetrical, 

 but ut many cases are dissimilar in form, aud more 

 particularly in the structure of the teeth, with which 



100 



101 



Figs. 99, Maxilla of the great water-beetle (Hydrous piceus) seen 

 from above; 100, from below; 101, from the back. 



the mandibles, from which they differ in their less firm 

 consistence and more complicated structure, being 

 formed of several parts,and especially by the possession 

 ofa slender articulated appendage or palpus, attached to 

 each. They appear to be more especially connected with 

 the lower lip, serving, iu some instances, as a sheath 

 for its defence ; in the beetles, however, they are 

 generally quite detached. In a table of the compa- 

 rative variation of the chief insect organs, Mr Mac 

 Leay has shewn that the maxillae are less liable to 

 vary than any other; hence it is important to note 

 the modifications to -which they are subject. 



The maxillae appear typically to consist of five 

 pieces, exclusive of the maxillary palpi, at least those 

 maxillae which are the most complicated in their 

 structure, exhibit this number of parts. They are the 

 cardo or hinge (figs. 99, 100, 101 a), a most appro- 

 priate term, designating a transverse horny piece by 

 which the jaw is affixed within the mouth by mem- 

 branes. Strauss calls this the branche transversale. 

 Savigny the support, Burmeister the base, and New- 

 man the insertio. This piece is especially distinct 

 in beetles and bees. The two following pieces (b fy c) 

 are closely soldered together, and compose the horny 

 pillar between the basal hinge and the terminal lobes. 

 Of these two parts, the external portion (c), as first 

 noticed by Latreille, and since named la piece ]:alj>ifite 

 by Strauss, and the squama by Burmeister, bears at its 

 extremity the maxillary palpus (/) ; the internal or 

 dorsal piece * (piece dorsal of Strauss-Durckheiun, b) 



* Mr. Newman appears to restrict the term maxillae to this 

 piece. 



