THE MOUTH-PARTS OF SOME BEETLE LARViE. 
375 
hypopharynx, an organ which has been almost entirely 
neglected by students of beetle-larvae. The result of our 
work, described in detail below, has been to establish the 
presence of maxillulas in the larvae of Dascillus, the first 
recognition, as we believe, of these interesting appendages 
in any stage of an Endopterygote (metabolic) insect. 
For comparison with Dascillus, we have examined many 
specimens of the larva of Helodes minuta, an aquatic 
member of the same famiH. This larva lives beneath sub- 
merged stones in hill-streams. Like that of Dascillus, it has 
a firm, well-chitinised cuticle, but while the Dascillus larva is 
stout in build, the Helodes grub is flattened like a woodlouse. 
In this flattening*, as explained fully below, the head and 
mouth parts are involved. The maxillulae, however, are in 
this larva even more distinct than in that of Helodes, their 
appendicular nature being beyond all possible doubt. We 
find that our description of these structures in Helodes has 
been anticipated by the researches of Rolpli (’74), who has 
treated the mouth-parts of this and allied larvae with some 
detail. We are glad, however, to confirm and extend his 
observations, and to establish the true nature, of the minute 
but highly interesting structures which he was the first 
to see. 
In the important paper already mentioned, Hansen ( J 03) 
gives reason for believing that the labial segment in insects 
was primitively a trunk-segment, and has become secondarily 
associated with the head, like the segment that bears the 
maxillipeds in the arthrostracous Crustacea. Huxley (’77, 
p. 403) had long previously suggested that the cervical 
sclerites of the cockroach belong to the labial segment. In 
the beetle larvse which we have examined we find support for 
this view. The external appearance of the Dascillus larva 
suggests that the labium is closely associated with the cuticle 
of the neck. And in all the larva3, except Helodes, which we 
have studied we find that the labium lies distinctly outside 
and behind the ventral sclerite of the liead-capsule (see 
Text-figs. 1, 2, 5). This fact is the more noteworthy because 
