STRUCTURE OF THE MOUTH. 259 
would have been dismembered, had the analogies of 
the group been sufficiently studied. The caudal 
appendages, then, of the Neuroptera assume dif- 
ferent forms, suited to their different offices: in the 
Forficula, or common earwig, they are used as means 
of defence; in the locusts, they are employed to 
perforate the ground for the deposition of the eggs ; 
and in the dragon-flies (Zzbellulide), they are con- 
nected with the process of impregnation. In the 
ephemera, they assume the appearance of three long, 
hair-like bristles, and really become tails, analogous, 
in appearance, to those of the ichneumon flies; but 
their particular use seems not clearly understood. 
Sufficient, however, has now been stated, to show 
the importance of using such characters in a generic 
sense; and wherever they occur in other groups, 
there will be no danger in employing them as the 
essential indication of sub-genera. 
(179.) Let us now consider the value of charac- 
ters founded upon the structure of the mouth. These, 
it is obvious, are, when rightly used, and constantly 
viewed in reference to the nature of the food, of the 
highest importance. Their value, however, entirely 
depends upon these considerations: if, for instance, 
we were to set out with placing all birds that live 
solely upon fruits in one division, all those which 
fed upon insects in another, the seed-eaters in a third, 
and so on, we should have an arrangement perfectly 
unintelligible. Again, if all flesh-eating birds were 
to be separated from such as eat fruits, we must ex- 
clude several of the American buzzards, which, as it 
is asserted, feed as much upon one as upon the 
other. Such deviations from the general character 
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