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 Papilionidse 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 

 liave been generally thought to deserve. 



In Mr. Trimen's paper on "Mimetic Analogies 



