THE MOUTH-PARTS OF SOME BEETLE-LARViE. 
383 
slender than that of the right. In position this jointed appen- 
dage is strikingly analogous to the cone-like structure found 
on the mandible of Helodes (PI. 35, fig. 4). 
The molar surface of the mandible is broad and strong, 
and forms a very powerful grinding* organ. Grahan (’08, 
p. 280) draws attention to the strong evidence of the vege- 
tarian habits of the larva which this basal molar tooth 
affords. The proximal surface is concave and ridged verti- 
cally. Its ventral basal tip is prolonged into a curious 
brush-like process (pr.), which is probably sensory in func- 
tion. This process is represented on a more rudimentary 
scale in Helodes. The convex dorsal aspect of the mandible 
usually bears spines. The mandible of the larva of Das- 
cillus Davidson ii, as described and figured by Rivers 
( ; 91, p. 93, pi. ii, 5, 5a), differs apparently but little from 
that of the D. cervinus larva. 
Each mandible articulates with the head skeleton by means 
of a condyle (c.) ventrally and a ginglymus ( g .) dorsally. 
The condyle is connected by a double ridge with a small pro- 
jecting boss ( b .) immediately behind the molar tooth and 
above the point of insertion of the tendon of the large 
adductor muscle. The condyle works in a socket on the 
ventral head skeleton. 
Musculature. 
There are two chief muscles controlling the mandibles — a 
large adductor or flexor (Ad., fig. 13), and a smaller abductor 
or extensor (Ah., fig*. 14). 
The adductor, the fibres of which pass to all parts of the 
head skeleton, is inserted by means of a curious large tendon 
( Td.) } formed of pale yellow cuticle, and shaped somewhat like a 
fan. To the edge of this fan-like tendon fibres pass from the 
hinder margin and dorsal aspect of the head skeleton, while 
those fibres which have their origin in the ventral plate of the 
head are inserted all over the ventral suface of the tendon, and 
have to be dissected away before the latter comes into view. 
