250 ANCESTR Y AND CLA SSIFICA TION. 



to the larva, by startling and frightening away 

 some enemy when about to seize it, and is thus 

 one of the causes which have led to the wide ex- 

 tension 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 advan- 

 tageous to its possessor, must see, in the posses- 

 sion of such an organ by one group and its com- 

 plete absence in every other, a proof of a very 

 ancient origin and of very long-continued modifi- 

 cation. 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 Papilionidae 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 gener- 

 ally thought to deserve." (Nat. Select., p. 135.) 

 It is unphilosophical, however, to accord high 

 rank to any group for a single characteristic, and 

 especially when in nearly all its other important 

 peculiarities it evinces its low origin. Moreover, 

 extensile fleshy scent organs do occur in other 

 groups. Guenee, as we have pointed out, discov- 

 ered them on the abdominal segments of the cater- 

 pillars of certain blues [see Figs. 34, 35] ; and 

 caruncles, as they are called, entirely similar to 



