Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

ILLUrSTRATIVE OF NATURAL SELECTION. 135
ordinary 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 successive variations, each one
advantageous to its possessor, must see, in the possession of such an organ by one group, and its
complete absence in every other, a proof of a very
ancient origin and of very long-continued modification. And such a positive structural addition to
the organization of the family, subserving an important function, seems to me alone sufficient to warrant
us in considering the Papilionidmn as the most highly
developed portion of the whole order, and thus in
retaining it in the position which the size, strength,
beauty, and general structure of the perfect insects
have been generally thought to deserve.
In 31r. Trimen's paper on' Mimetic Analogies