ILLUSTRATIVE 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 sud- 
denly thrown: out by the insect when alarmed. When 
we consider this singular apparatus, which in some 
species is nearly half an inch long, the arrange- 
ment 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 con- 
clusion 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 per- 
manence 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 pos- 
session 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 modifica- 
tion. And such a positive structural addition to 
the organization of the family, subserving an impor- 
tant function, seems to me alone sufficient to warrant 
us in considering the Papilionide 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 Mr. Trimen’s paper on “Mimetic Analogies 
