XV 



the conception of the existence of such a strongly separated horodimorphism 

 has become his hobby ; continually at it, involving others in it and being backed 

 up by the dealers in insects to whom this is profitable. Now I certainly do 

 not dispute the possibility that in a continental climate like that of British India 

 such differences perhaps appear more strongly than in the climate of the islands 

 of the Indian archipelago, but it is certain that in those islands they are not 

 so distinct and cannot be so either. In the first place there are sometimes 

 regions where the seasonal rain falls and those where this is not the case at 

 the same time close to each other. In the south-western peninsula of Celebes 

 the mountains seem to form the boundary. While south-east of them the seasonal 

 rain falls, the dry season prevails west of them, and the reverse; near Ban- 

 taeng (Bonthain) these two regions are contiguous to each other. 



Probably the same phenomenon occurs in West-Java with regard to the 

 northern and the southern part, which are also separated by a high mountain- 

 range. More than once I saw collections of Lepidoptera which were clearly 

 characterized by their richness of species and strong development of the indi- 

 viduals, as being collected in the rainy season, from the regions on the south- 

 coast near Pelabouan Ratou (Wijnkoopsbay), where they had been caught in 

 July and August, when North Java is in the middle of the dry season. To 

 distinguish those forms, it is therefore necessar}' to know exactly when and 

 where each of them was caught in some island, and when the dry and the 

 wet season prevail in the different districts of this island. Besides those seasons 

 are very irregular. This is the same case with the seasons in a coast-land 

 Hke Holland, where very warm summers and very cold winters are rare, where 

 a great part of the winter is temperate and a great part of the summer bleak. 

 So also in Java f i., especially in West-Java very dry or very wet seasons 

 are an exception. Often there are many dry days during the rainy season 

 and rain falls every now and then during the dr)' season. It also seems that 

 in some parts, as in N. E. Sumatra, it rains all the year round every now 

 and then. Where a rainy season exists, it is certain that the humidity is 

 greater, and this causes a more abundant flora and in connection with this 

 also a more abundant fauna of butterflies. The more humidity there is, the 

 stronger the plant and its different parts and consequently each leaf indepen- 

 dently develops itself; so it is very probable that also the nutritive power will 

 increase; the caterpillars which are caught in a strong rainy season make the 

 impression of being extremely well fed and therefore big and strong specimens. 

 We must not forget, moreover, that in the dense woods of the high mountains 

 which are always the greater part of the day enveloped in clouds, the whole 

 flora is always in a very damp state. 



