324 NATURAL HISTORr [chap.xiv. 



case had the lands been actually united. Such groups as 

 the bower birds (Ptilonorhynchus), the black and red 

 cockatoos (Calyptorhynchus), the blue wrens (Malurus), the 

 crowshrikes (Cracticus), the Australian shrikes (Falcun- 

 culus and Colluricincla), 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 approached nearer to it than twenty 

 miles. Neither do any of the most characteristic groups 

 of Australian insects occur in Timor ; so that everything 

 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 equality in the numbers of identical and representa- 

 tive species derived from each extremity. It is true that 

 the widening of the strait at the Australian end by sub- 

 sidence, would, by putting a stop to immigration and inter- 

 crossing of individuals from the mother country, have 

 allowed full scope to the causes which have led to the 

 modification of the species ; 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 character of the fauna of the 



