258 STUDY OF NATURAL HISTORY. 



pendages to the body, always indicate a sub-genus, 

 and will sometimes point out groups of a higher 

 denomination. It is remarkable that the lower wings 

 of the Lepidoptera, when thus unusually lengthened, 

 perform the same office in flight as the tail does 

 among birds, for we find that all the swiftest flying 

 butterflies have what are aptly and justly called 

 swallow-tailed wings ; that is to say, their extremities 

 are lengthened out into tail-like processes. The 

 sub -gen era JPodalirius, Protesilaus, Leilus, and 

 Eudamus (all of which are figured and charac- 

 terised in the Zool. Illustr. 2d series), are striking 

 examples of this form, and the Eudamus borealis 

 (Hesp. proteus Lin.) is such a common species 

 that almost every cabinet contains an example. 

 Essential characters, therefore, may safely be drawn 

 from this structure, for its universality among the 

 classes of insects and of birds leads us to infer it 

 is one of those primary types of variation which 

 nature has herself chosen. On looking to the other 

 orders of winged insects, we find but few examples 

 of elongated lower wings, and these are chiefly con- 

 fined to the Neuroptera Lin. : but here we find 

 that caudal appendages are almost universal, so that 

 they nearly become one of the essential and natural 

 . characters of the whole order. The entomologist 

 will observe that we are now speaking of the Neur- 

 optera, as defined by Linnaeus ; and not of that 

 section of it only to which modern systematists, on 

 views the most artificial, have restricted the name. 

 It will be hereafter shown that this order, as con- 

 templated by Linnaeus, is one of the most natural in 

 the whole circle of the Annulosce; and that it never 



