500 Records of the Indian Museum. (VoL. XI, 
the tissues of the leaf appear to offer no resistance, but as the 
maxilla passes back into the cavity between the mandible and 
labral process close to the concave part of the serrate margin of 
the latter, there is probably some amount of scissor action between 
them. 
The mandible closely follows the maxilla in all its movements, 
and forms a sheath above it. Precisely to what extent it func- 
tions as a biting organ is most difficult to see with certainty. Its 
smooth dorsal face works along the serrate transverse edge of the 
labrum from end to end, and its distal end slides past the serrate 
longitudinal edge of the labral process as it follows the maxilla 
into the cavity behind. Probably the mandible makes all the 
transverse cuts that are required, and it could no doubt make 
longitudinal cuts as well should the maxilla fail to work properly ; 
but no transverse cutting seems to be left for it under ordinary 
circumstances, and the tracks of the maxillary teeth can be dis- 
tinctly seen on each freshly bitten surface. One of the chief func- 
tions of the mandible appears to be to protect these teeth, when 
they are not in use, by closing in the cavity between the labrum 
and the labium, in which they lie when at rest. 
Intervals of varying length between the bites are devoted 
to mastication. During this process the gnathites of the two sides 
work simultaneously as before, but the maxillae are not exserted 
—i.e. they remain in the cavity between the mandibles, their 
extremities being exposed between (and posterior to) the man- 
dibles and the labral process each time they are opened. At the 
same time the labral process and labium are alternately separated a 
little and brought together again. Mastication presumably takes 
- place chiefly between the large molar teeth, situated one at the 
base of each mandible (pl. xxii, fig. 6), the triangular thickened 
area on the inner side of the labium (pl. xxii, fig. 6), and the 
somewhat similar convexity on the inner side of the labrum. It 
is possible, however, that the terminal teeth of the maxilla take 
some part in it also, for those of opposite sides are not quite alike, 
and when pressed together after removal of the labrum, the teeth 
of one side may be seen to fit into the spaces between the teeth on 
the other, although the teeth can never be brought together thus 
during the process of biting. 
This method of feeding differs in several respects from the 
method of feeding observed by Obaus (Stett. Ent. Zeit., 1909, 
pp. 12-13) in Rutelinae of the Geniates group, South American 
insects whose mouth is also divided longitudinally into two parts. 
Geniates and its allies always cling to both sides of the leaf at the 
same time instead of to one side only, commencing to feed at the 
edge instead of on the upper or under side; they also exude such 
large quantities of saliva that it escapes from the mouth and 
stains the bitten margin of the leaf—a thing which has never been 
observed in A doretus. 
The difference in the method of biting the leaf is associated 
with differences in the structure of the mouth parts. Geniates 
