4.24 EXTERNAL ANATOMY OF INSECTS. 
two, three, or more lobes*; the intermediate one more 
directly answering to the /abium of other insects, and the 
basal one or mentum. This organ in the Libellulina is 
of a different structure: it has only two articulations 
representing /abium and mentum ; but the former consists 
of three parallel pieces, the two exterior ones rising 
higher than the intermediate one, and at their inner 
angle having an acute sinus from which the palpi emerge ; 
and the intermediate piece, which is longitudinally chan- 
nelled, lapping over the inner side of the lateral pieces. 
From the angle of the covered part of these pieces, a 
subulate short horizontal horn points inwards towards 
the tongue, which it must keep from closing with the 
labium >. 
3. Palpi Labiales *.—The last-mentioned organs, the 
labial palpi, next claim our attention: but before I ad- 
vert particularly to them, it will be proper to premise a 
few words upon palpi, or feelers, in general. These are 
usually jointed moyeable organs, of a corneous or coria- 
ceous substance, attached by ligaments to the Jabéwm and 
maxilla, and in the Crustacea even to the mandibule. 
Their joints, which are usually more or less obconical, 
articulate also in each other by ligaments, with perhaps 
some little mixture of the ball and socket. Their ends, 
the last joint especially, seem furnished with nervous 
papille which indicate some peculiar sense, of which 
they are the instrument. What that sense is has not 
been clearly ascertained, and concerning which I shall 
a Puate VI. Fic. 6G. b!. ® Ibid. Fic. 12. b’. 
© Prates VI. VII. XXVI. b”. 
