THE MOUTH-PARTS OE SOME BEETLE LARVAE 
387 
hypopharynx is exposed (Text-fig. 1). This condition lends 
strong support to the theory (see “ Introduction/’ p. 373) 
that the labial appendages belong to a segment primitively 
thoracic, which in development becomes associated with the 
head. It is most interesting to find the same conditions in 
Geotrupes and Phyllopertha (see below). 
The absence of the ventral head sclerite in Helodes is 
probably due to the dorsi-ventral flattening and lateral 
displacement of the mouth-parts. 
Text-fig. 1. 
Dascillus cervinus. Head of larva, ventral view. The labium 
and associated cervical sclerites (a) together with the maxillae 
have been removed so as to expose the ventral sclerite ( v . s.) of 
the liead-capsule and the hypopharynx (hyp.), x 16 . 
The Larva] of Geotrupes and Phyllopertha. 
The jaws of these two larvae have been described and 
figured by other observers, notably Schiodte (’74, pp. 336-340, 
307-310, pis. xvi, figs. 1—1 8, xii, figs. 8-14), so that it is only 
necessary to draw attention to those facts of structure which 
are of significance with regard to the conclusions of this paper. 
As far as we can find out the tongues have hot as yet been 
studied, so that it seems well to describe and figure them in 
some detail. 
In both the larvae the head skeleton is quite continuous 
beueath the labium, and the neck-sclerites are markedly 
posterior in position (see Text-figs. 2, 3). 
