OF THE MOUTH PARTS OF CERTAIN INSPXTS. 191 



In all the species heretofore cited the galear joints were more or less distinct and 

 the psendoti'acheal system was little or not at all developed. As the face of the joints 

 Ijecomes covered by a ridged membrane the textui'e of the entire sti'ucture chang-es. 

 It becomes less chitinized, and the chitine is not evenly distributed, causing sutures to 

 Ijccome indistinct and pooi'ly marked. Yet, keeping in mind the general line of varia- 

 tion, we can usually reach a correct conclusion. 



In a Leptid, species unknown, we find the appearance shown in PI. II, Fig. 1. 

 Here there is a united basal plate, covered on one surface with a membrane, and from 

 the cliitinous 2)ortion arises the palpifer with its attached palpus. Surmounting the 

 chitinous base are two joints, the galea, the ehitinous parts of which only ai'c shown 

 in outline, the balance of the space being co\ered by membrane. Hei"e again the 

 attachment of the maxillary palpus to the basal sclerite determines the maxillary char- 

 acter of all the sclerites dii-ectly articulated to it. 



In Iltrmetia mucen< ( PI. II, Fig. 17) the entiie structure is much more membi-an- 

 ous, jQt the basal chitinous })late is paired, and while the parts are shown in a dis- 

 torted position, the two galear joints and their relation to the basal, palpus-bearing 

 structure is yet pei-fectly obvious. The other maxillary structures have coini)letely 

 disappeared, Avhile what is left of the labium is seen at PI. Ill, Fig. 14. 



The mouth parts in some si)ecies of Tlju'la are interesting, and a fair illustration 

 of one of the "snub-nosed" species is seen at PI. I, Fig. 5. Here the origin of the 

 paljius at the immediate base of the chitinized part of thelabella indicates its character, 

 and if we divest the chitine of the surrounding membi'anewe get the appearance shown 

 at Fig. 5". Pi-actically we have a completely paired organ, the relations of which are 

 perfectly simple when the confusing and unim[)ortant meml)rane is removed. 



The peculiar relation of labrum and lal)ium in the Ein>niliK has been already 

 noted, and this makes it easy to separate olf all the other parts adhering to the margin 

 of the head, but not in any way connected with the labium. The relation of the parts 

 to each other in F.mpis sjjectahilis is shown on PI. II, Fig. 13, while on PI. Ill, Fig. 2', 

 are shown the maxillary sti'ucturcs o^ l\li(nnj>liomy!ji lonyicauda. In this lattei' figure 

 we note that the ])arts, except palpifer, are entirely membranous. From tlie basal 

 sclerite the palj)i arise so a< to form only a continuation of the membrane itself with 

 an extremely slight attachment to the chitinous paljjifer : and to this very same mem- 

 l)i'ane there is articulated by a slightly thickened sutui'c the subgalea, united poste- 

 riorly, but separated in front; and this bears in turn tlie indistinctly segmented gali'a. 

 This entire structure obviously belongs together and is one organ — necessarily the 

 maxilla. 



A very similar structure is found in C/a/v/so/as- (PI. II, Fig. 11) ami in other species 



