OF THE MALAYAN REGION. 19 



any knowledge ; and though we may not be able to trace it satisfactorily, there can, I 

 think, be little doubt that the singxilar modification in the wings of so many of the 

 butterflies of that island is an effect of that complicated action and reaction of all living 

 things upon each other in the struggle for existence, which continually tends to readjust 

 disturbed relations, and to bring every species into harmony with the varying conditions 

 of the surrounding universe. 



But even the conjectural explanation now given fails us in the other cases of local modi- 

 fication. T\Tiy the species of the western islands should be smaller than those fr.rther east, 

 — why those of Amboyna should exceed in size those of Gilolo and New Guinea — why 

 the tailed species of India should begin to lose that appendage in the islands, and retain 

 no trace of it on the borders of the Pacific, are questions which we cannot at present 

 attempt to answer. That they depend, however, on some general principle is cctain, 

 because analogous facts have been observed in other parts of the world. Mr. Bates 

 informs me that, in three distinct groups, PapUios which on the Upper Amazon and in 

 most other parts of South America have spotless upper wings obtain pale or white spots 

 at Para and on the Lower Amazon ; and also that the ^«ea«-group of Papilios never have 

 tails in the equatorial regions and the Amazons valley, but gradually acquii-e tails in many 

 cases as they range towards the northern or southern tropic. Even in Europe we have 

 somewhat similar facts ; for the species and varieties of butterflies peculiar to the island 

 of Sardinia are generally smaller and more deeply coloured than those of the mainland, 

 and Pajnlio Hospiton has lost the taU, which is a prominent feature of the closely allied 

 P. Machaon. 



Facts of a similar nature to those now brought forward would no doubt be found to 

 occur in other groups of insects, were local faunas carefully studied in relation to those 

 of the surrounding countries ; and they seem to indicate that climate and other physical 

 causes have, in some cases, a very powerful efi'ect in modifying specific form, and thus 

 directly aid in producing the endless variety of nature. 



I may state that I can adduce facts perfectly analogous to these from other families of 

 Lepidoptera, especially the Danaidse ; but as the greater part of the species are stUl unde- 

 scribed, I can only now assert that similar phenomena do occur there. 



Mimicry. 



I need scarcely say that I entirely agree with Mr. Bates's explanation of the 

 causes which have led to one group of insects mimicking another (Trans. Linn. Soc. 

 vol. xxiii. p. 495). I have, therefore, only now to adduce such illustrations of this 

 curious phenomenon as are fiu'nished by the Eastern Papilionida?, and to show their 

 bearing upon the phenomena of variation already mentioned. As in America, so in the 

 Old World, species of Danaidae are the objects which the other families most often 

 imitate. But, besides these, some genera of Morphidse and one section of the genus 

 Papilio are also less frequently copied. Many species of Papilio mimic other species 

 of these three groups so closely that they are undistinguishable when on the wing ; and 

 in every case the pairs which resemble each other inhabit the same locality. 



The following list exhibits the most important and best -marked cases of mimicry which 

 occur among the Papilionidae of the Malayan region and India : — 



d2 



