IN TROD UC riON Ix v 



mountains and under very diverse conditions. It is clearly only restricted from 

 reaching the coast by the presence of introduced predaceous insects, which quickly 

 exterminate it, and doubtless it did once frequent the coastal region. It is one of 

 the few beetles found in the dry branches or stems of those trees, which form a 

 large part of the island driftwood, and being able to adapt itself to very varied 

 conditions of climate etc. and also breeding freely in those trees, which extend right 

 down to the coast, it must have had unusual opportunities for being carried across 

 the interisland channels and also for becoming established when so transported. 

 It even breeds abundantly in the dry, woody capsules of some xerophilous trees. 

 I should consider in this case that the interisland channels have not been sufficient 

 to isolate examples, that may have reached the different islands. Though flightless, 

 we may class such a species with the vagrant birds, Hmmtione, Psittacirostra etc. 

 elsewhere alluded to. 



It is interesting to observe in animals in which secondary sexual characters of 

 the male are conspicuous, that when geographical isolation has taken place, these 

 are generally modified, in fact herein may apparently be the only modification, as 

 if these sexual characters were often the first to become changed. 



It should be noted that specific change may be concurrent with isolation alone, 

 without any change of food or habits, so far as can be observed, though, of course, 

 whether there is really a change of habits is uncertain. 



Quite apart from these cases, where isolation on separate islands has induced 

 specific change, we must consider the cases where extremely closely allied species 

 derivatives one from the other, or both from a form hardly different from either, 

 exist on the same island. Of these there are two classes, one in which the closely 

 allied species inhabit only different areas, and the other in which they occupy the 

 same area. In the first case the species are on the same footing as if they inhabited 

 different islands. The best illustration of these is shown by the land Mollusca, of 

 which it is often said that each valley on Oahu has its own peculiar species. It is 

 true that many of the valleys do apparently have their own species, or at least local 

 races, which do not pass beyond, but there are numerous species that have a much 

 more extensive range, either occupying several valleys or ridges, or even having 

 a still wider distribution. It is not accurately known how the Achatinella are 

 distributed, but it is quite clear that they can only pass from island to island by 

 a most rare and exceptional chance. This is shown by their poor representation 

 on Hawaii and Kauai, and the fact that of the arboreal species on such islands as 

 Oahu, Molokai and Maui (where they are well represented) there is on each island 

 a specific multiplication of only a few type forms, showing that the present numerous 

 species on a particular island are the produce of only a few earlier established forms. 

 The ' Apex ' group of Achatinella is peculiar to Oahu, and so with other groups. 

 The sluggishness of the animals would probably make any wide distribution of the 

 F. H. I. i 



