OF THE MOUTH PARTS OF CERTAIN INSECTS. 191 
Jn all the species heretofore cited the galear joints were more or less distinct and 
the pseudotracheal system was little or not at all developed. As the face of the joints 
becomes covered by a ridged membrane the texture of the entire structure changes. 
It becomes less chitinized, and the chitine is not evenly distributed, causing sutures to 
become indistinct and poorly marked. Yet, keeping in mind the general line of yaria- 
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 chitinous portion arises the palpifer with its attached palpus. Surmounting the 
chitinous base are two joints, the galea, the chitinous parts of which only are shown 
in outline, the balance of the space being covered by membrane. Here again the 
attachment of the maxillary palpus to the basal sclerite determines the maxillary char- 
acter of all the sclerites directly articulated to it. 
In Hermetia mucens (PI. II, Fig. 17) the entire structure is much more membran- 
ous, yet the basal chitinous plate 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 perfectly obvious. The other maxillary structures have completely 
disappeared, while what is left of the labium is seen at Pl. III, Fig. 14. 
The mouth parts in some species of Zvpula are interesting, and a fair illustration 
of one of the “snub-nosed”’ species is seen at Pl. I, Fig. 5. Here the origin of the 
palpus at the immediate base of the chitinized part of the labella indicates its character, 
and if we divest the chitine of the surrounding membrane we get the appearance shown 
at Fig. 5" Practically we have a completely paired organ, the relations of which are 
perfectly simple when the confusing and unimportant membrane is removed. 
The peculiar relation of labrum and labium in the Hmpide has been already 
noted, and this makes it easy to separate off 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 Hmpis spectabil’s is shown on Pl. I, Fig. 13, while on PI. III, Fig. 2’, 
are shown the maxillary structures of Rhamphomyia longicauda. In this latter figure 
we note that the parts, except palpifer, are entirely membranous. From the basal 
sclerite the palpi arise so as to form only a continuation of the membrane itself with 
an extremely slight attachment to the chitinous palpifer ; and to this very same mem- 
brane there is articulated by a slightly thickened suture the subgalea, united poste- 
riorly, but separated in front; and this bears in turn the indistinctly segmented galea. 
This entire structure obviously belongs together and is one organ—necessarily the 
maxilla. 
A very similar structure is found in Chrysops (Pl. LI, Fig. 14) and in other species 
