178 THE MALAYAN PAPILIONIDE AS 
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,—and why, in three separate 
cases, the females of Amboyna species should be less 
gaily attired than the corresponding females of the 
surrounding islands,—are questions which we cannot 
at present attempt to answer. That they depend, how- 
ever, on some general principle is certain, because ana- 
logous 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 Para and on the 
Lower Amazon; and also that the Alneas-group of Pa- 
pilios 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 the 
same has recently been shown to be the case with the 
common tortoiseshell butterfly in the Isle of Man; 
while Papilio Hospiton, peculiar to the former island, 
has lost the tail, which is a prominent feature of the 
closely allied P. Machaon. 
Facts of a similar nature to those now brought for- 
ward would no doubt be found to occur in other 
groups of insects, were local faunas carefully studied in 
