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 (Lihellulidiz), 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 

 s 2 



