958 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-genera Podalirius, 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 Linneus; 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 Linnzus, is one of the most natural in 
the whole circle of the Annulose; and that it never 
