164 Phenomena of Variation and Geographical Distribution, 



degree of certainty caii be attached. The spur on the anterior tibise 

 is also found in some of the Hesperidffi, 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 

 Papilionidoe, however, and that on which I think insufficient stress 

 has been laid, is undoubtedly the peculiar structure of the larvse. 

 These all possess an extraordinary organ situated on the neck, the 

 Avell 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 color, 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 larvae, by startling and frightening away some 

 enemy when about to seize it, and is thus one of the causes Avhich 

 has led to the wide extension and maintained the permanence of this 

 now dominant group. Those who believe that such peculiar struc- 

 tures 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 a very long continued modifica- 

 tion. 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 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 struc- 

 ture of the perfect insects have been genex'ally thought to deserve. 



The PapilionidtB are pretty widely distributed over the earth, but 

 are especially abundant in the tropics, Avhere they attain their maxi- 

 mum of size and beauty, and the greatest variety of form and coloring. 

 South America, North India, and the Malay Islands are the regions 

 where these fine insects occur in the greatest profusion, and where 

 they actually become a not unimportant feature in the scenery. In 

 the Malay Islands in particular the giant OrnithojDterse may be fre- 

 quently seen about the borders of the cultivated and forest districts, 

 their large size, stately flight, and georgeous coloring rendering them 

 even more conspicuous than the generality of birds. In the shady 

 suburbs of the town of Malacca two large and handsome Papilios 

 {Memnon and Nephelus) are not uncommon, flapping with irregular 

 flight along the roadway, or, in the early morning, expanding their 



