Of the Timor Group. 215 



cla), and many others, which abound all over Australia, 

 would certainly have spread into Timor if it had been united 

 to that country, or even if for any long time it had approach- 

 ed nearer to it than twenty miles. Neither do any of the 

 most characteristic groups of Australian insects occur in Ti- 

 mor ; so that every thing combines to indicate that a strait 

 of the sea has always separated it from Australia,^ but that 

 at one period this strait was reduced to a width of about 

 twenty miles. 



But at the time when this narrowing of the sea took place 

 in one direction, there must have been a greater separation 

 at the other end of the chain, or we should find more equal- 

 ity in the numbers of identical and representative species de- 

 rived from each extremity. It is true that the widening of 

 the strait at the Australian end by subsidence would, by 

 putting a stop to immigration and intercrossing of individ- 

 uals from the mother-country, have allowed full scoj)e to the 

 causes which have led to the modification of the s^Decies ; 

 while the continued stream of immigrants from Java would, 

 by continual intercrossing, check such modification. This 

 view will not, however, explain all the facts ; for the charac- 

 ter of the fauna of the Timorese group is indicated as well 

 by the forms which are absent from it as by those Avhich it 

 contains, and is by this kind of evidence shown to be much 

 more Australian than Indian. No less than twenty-nine 

 genera, all more or less abundant in Java, and most of which 

 range over a wide area, are altogether absent ; while of the 

 equally diffused Australian genera only about fourteen are 

 wanting. This would clearly indicate that there has been, 

 till recently, a wide separation from Java ; and the fact that 

 the islands of Bali and Lombock are small, and are almost 

 wholly volcanic, and contain a smaller number of modified 

 forms than the other islands, would point them out as of 

 comparatively recent origin. A wide arm of the sea proba- 

 bly occupied their place at the time when Timor was in the 

 closest proximity to Australia ; and as the subterranean fires 

 were slowly piling up the now fertile islands of Bali and 

 Lombock, the northern shores of Australia would be sink- 

 ing beneath the ocean. Some such changes as have been 

 here indicated enable us to understand how it happens that. 



