88 CERTAIN PARASITIC INSECTS. 
dibles and maxille arise near each other in the middle of 
the head opposite the eyes, their bases slightly diverging. 
Thence they converge to the mouth over which they meet 
and beyond are free, being hollow, thin bands of chitine, 
meeting like the maxille, or tongue, of butterflies to form 
a hollow tube for suction. The mandibles each suddenly 
end in a curved, slender filament, which is probably used 
as a tactile organ to explore the best sites in the flesh of 
their victim for drawing blood. On the other hand the 
maxille, which are much narrower than the mandibles, be- 
come rounded towards the end, bristle-like, and tipped with 
Fig.16. — ,numerous exceedingly fine barbs, by which the 
E bug anchors itself in the flesh, while the blood 
is pumped through the mandibles. The base 
~ of the large, tubular labium, or beak, which 
ensheathes the mandibles and maxille, is op- 
posite the end of the clypeus or front edge of 
the upper side of the head, and at a distance 
beyond the mouth equal to the breadth of the 
Body Louse. ]abium itself. The labium, which is divided 
into three joints becomes flattened towards the tip, which 
is square, and ends in two thin membranous lobes, prob- 
ably endowed with a slight sense of touch. On comparing 
these parts with those of the louse it will be seen how 
much alike they are, with the exception of the labium, a 
very variable organ in the Hemiptera. From the long 
sucker of the Pediculus, to the stout chitinous jaws of the 
Mallophaga, or bird lice, is a sudden transition, but on com- 
paring the rest of the head and body it will be seen that the 
distinction only amounts to a family one, though Burmeister 
placed the Mallophaga in the Orthoptera on account of the 
mandibles being adapted for biting. It has been a common 
source of error to depend too much on one or a single set of 
organs. Insects have been classified on characters drawn 
from the wings, or the number of the joints of the tarsi, or 
the form of the mouth parts. We must take into account in 
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