Mouth Organs of Insects. 53 
the paraglosse (Fig. 35, @), one on eithe: side. These 
are often wanting. 
The jaws or mandibles ( Fig. 8, , mz) arise one on either 
side just below and at the side of the labrum, or upper lip. 
These work sidewise instead of up and down as in higher 
animals, are frequently very hard and sharp, and sometimes 
armed with one or more teeth. A rudimentary tooth 
(Fig. 12, @, 6) is visible on the jaws of drone and queen 
bees. 
Beneath the jaws or mandibles, and inserted a little far- 
ther back, are the second jaws, or maxilla (Fig. 8, 7, x), 
less dense and firm than the mandibles, but far more com- 
plex, Each maxilla arises by a small joint, the cardo; next 
this is a larger joint, the stipes; from this extends on the 
inside the broad lacinia (Fig. 35, c) or blade, usually fringed 
with hairs on its inner edge, towards the mouth; while on 
the outside of the stipes, is inserted the—from one to seve- 
ral jointed—maxillary palpus. In the honey-bee the max- 
illary palpi are very small ‘and consist of two joints, and in 
some insects are wholly wanting. Sometimes, as in some 
of the beetles, there is a third piece running from the stipes 
between the palpus and lacinia called the galea. The max- 
ill also move sidewise, and probably aid in holding and 
turning the food while it is crushed by the harder jaws, 
though in some cases they, too, aid in triturating the food. 
These mouth-parts are very variable in form in different 
insects. In butterflies and moths, two-winged flies and bugs, 
they are transformed into a tube, which in the last two 
groups forms a-hard, strong beak or piercer, well exem- 
plified in the mosquito and bed-bug. In all the other 
insects we find them much as in the bees, with the sepa- 
rate parts varying greatly in form, to agree with the habits 
and character of their possessors. No wonder DeGeer 
and Fabricius detected these varying forms as strongly 
indicative of the nature of the insect; and no wonder that 
by their use they were so successful in forming a natural 
classification. 
If, as is more thap probable, the “ Doctrine of Selection ” 
is well founded, then a change in habit is the precursor of 
a change in structure. But what organs are so intimately 
