﻿A SWARM OF BUTTERFLIES IN SARAWAK. 155 



records " vast numbers of butterflies, in bands or flocks of count- 

 less myriads, extended as far as the eye could range," when he 

 was in the * Beagle ' some miles off the mouth of the Plata. 

 Then there is Lyell's well-known account of Vanessa cardui, of 

 which he writes * : " A vast swarm of this species, forming a 

 column from ten to fifteen feet broad, was in 1826 observed in 

 Switzerland, in the Canton de Vaud; they traversed the country 

 with great rapidity from north to south, all flying onwards in 

 regular order, close together, and not turning from their course 

 on the approach of other objects." 



If our Sarawak swarms were migrating to the mainland, we 

 may presume they would interbreed with their emalea cousins 

 there. I should state, by the way, that the geographical dis- 

 tribution of Cirrochroa emalea, Gu6v. is South Tenasserim, Malay 

 Peninsula, Nias Island, Sumatra, Java, and Borneo. In each of 

 these countries slightly different forms are found, which some 

 writers (Fruhstorfer in Seitz's ' Macro-Lepidoptera of the World ' 

 is the latest) name as distinct subspecies. That from Java 

 (bajadeta, Moore), and that from Nias {lapaona, Kheil), appear 

 to be well-separated geographical races, but the forms occurring 

 in the Malay Peninsula, Sumatra, and Borneo are scarcely 

 separable ; and Fruhstorfer's subspecific distinctions seem to 

 rest on very variable characters ; the white discal fascia on the 

 hind wing below, for instance, is very variable in a Sarawak 

 series before me. If these migrating swarms are not strictly 

 local, but wider migrations (and perhaps not infrequent) between 

 the three countries — the Malay Peninsula, Sumatra, and Borneo 

 — then we must look with more suspicion than ever on these 

 particular subspecific distinctions. 



It has long been noticed that the fauna of these three 

 countries, for which I propose the collective name Neomalaya, 

 has a remarkable number of species in common compared with 

 the fauna of the neighbouring island of Java, which shows a 

 closer relationship in some ways to the fauna of Eastern India 

 than it does to these three much nearer Malayan countries. The 

 explanation of this is that Java has been separated as an island 

 for a very much longer period, while the other three countries 

 have formed one continuous land-mass at a more recent period. 

 But, on the other hand, each of these three countries has been 

 separate for a sufficiently long period to develop quite a respect- 

 able endemic fauna for itself; so that it is a little difficult some- 

 times to account for the similarity of individuals in the three 

 countries on the geological explanation alone. Especially is this 

 the case when everything points to the species being peculiarly 

 liable to develop local but constant variations. I suggest that 

 migration plays a bigger part than we are apt to remember in 



- 'Principles of Geology,' vol. ii. p. 381 (12th edition 1875). 



