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 singular 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. Why the species of the western islands should be smaller than those farther 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 Pacifie, are questions which we cannot at present 
attempt to answer. That they depend, however, on some general principle is certain, 
because analogous facts have been observed in other parts of the world. Mr. Bates 
informs me that, in three distinct groups, Papilios which on the Upper Amazon and in 
most other parts of South America have spotless upper wings obtain pale or white spots 
at Pará and on the Lower Amazon; and also that the Æneas-group of Papilios never have | 
tails in the equatorial regions and the Amazons valley, but gradually acquire 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 Papilio Hospiton has lost the tail, 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 
oceur 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 effect 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 Danaide ; but as the greater part of the species are still unde- 
scribed, I can only now assert that similar phenomena do occur there. 
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 furnished by the Eastern Papilionidæ, and to show their 
bearing upon the phenomena of variation already mentioned. As in America, so in the 
Old World, species of Danaide are the objects which the other families most often 
imitate. But, besides these, some genera of Morphidæ and one section of the genus 
Papilio are also less frequently copied. Many species of Papilio mimie 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 mimiery which 
occur among the Papilionidæ of the Malayan region and India :— 
D 2 
