merely in the imperfection or abortion of certain organs, can establish
in the group exhibiting it a claim to a high grade of organization,
still less can this be allowed when another group along with perfection
of structure in the same organs, exhibits modifications peculiar to it,
together with the possession of an organ which in the remainder of the
order is altogether wanting. This is, however, the position of the
Papilionidae. The perfect insects possess two characters quite peculiar
to them. Mr. Edward Doubleday, in his "Genera of Diurnal Lepidoptera,"
says, "The Papilionidae may be known by the apparently four-branched
median nervule and the spur on the anterior tibiae, characters found in
no other family." The four-branched median nervule is a character so
constant, so peculiar, and so well marked, as to enable a person to
tell, at a glance at the wings only of a butterfly, whether it does or
does not belong to this family; and I am not aware that any other group
of butterflies, at all comparable to this in extent and modifications of
form, possesses a character in its neuration to which the same degree of
certainty can be attached. The spur on the anterior tibiae is also found
in some of the Hesperidae, and is therefore supposed to show a direct
affinity between the two groups: but I do not imagine it can
counterbalance the differences in neuration and in every other part of
their organization. The most characteristic feature of the Papilionidae,
however, and that on which I think insufficient stress has been laid, is
undoubtedly the peculiar structure of the larvae. These all possess an
extraordinary organ situated on the neck, the well-known Y-shaped
tentacle, which is entirely concealed in a state of repose, but which is
capable of being suddenly thrown out by the insect when alarmed. When we
consider this singular apparatus, which in some species is nearly half
an inch long, the arrangement of muscles for its protrusion and
retraction, its perfect concealment during repose, its blood-red colour,
and the suddenness with which it can be thrown out, we must, I think, be
led to the conclusion that it serves as a protection to the larva, by
startling and frightening away some enemy when about to seize it, and is
thus one of the causes which has led to the wide extension and
maintained the permanence of this now dominant group. Those who believe
that such peculiar structures can only have arisen by very minute
su