INTRODUCTION Ixi 



an age of Cicindelidae (of which also a few are found in Fiji), no age of Composites 

 or tree-lobeh'as any more than an age of Drepanididae (birds) or Plagithmysides 

 (beetles). Where conditions have proved favourable and remained so, and plant or 

 animal has become adapted to special conditions, an exuberance of distinct forms 

 has sprung from the ancient immigrant. Such cases are manifest in the Lobeliaceae 

 amongst plants, and in many groups of animals, the Drepanididae (birds), Plagithmysidae 

 (insects), Achatinellidae (moUusca) and many others. Such form the chief and most 

 interesting part of the native fauna and flora of the present day. 



Species-formation in the Hawaiian animals. 



As evidenced by the long series of closely allied endemic species of many kinds 

 of animals, it is clear that species-formation has been very active within the limited 

 area of the islands and there is no reason to doubt that this activity still continues. 

 Some insight into the possible modes by which this multiplication of species has 

 taken place may be gained by a consideration of the existing fauna. But what is 

 now needed is not so much general, or even special collecting of existing forms, as 

 years of e.xperimental work in breeding a well-selected series of animals in the field. 

 Unfortunately this cannot be done by residents in the settlements on the coast, but 

 needs a prolonged and continuous residence in the mountain forests. In few cases 

 can the mountain creatures be acclimatized to breed successfully in the lowlands, 

 and it would be folly to embark on a laborious series of experiments, destined to fail, 

 as soon as results were becoming interesting, if not sooner. 



Geographical segregation we may judge to have been a most important factor 

 in the evolution of species within the islands. It is obvious that the magnitude of 

 the total number of species of animals is to a large extent due to the fact that, 

 instead of one continuous land area, there are six forest-clad islands, and that in 

 many very large genera very few identical species are found on more than one, and 

 many others in only two or three of these islands. Thus the bird genus Oreomyza 

 (Pis. XIII and XIV) has a distinct species on each island. These birds have mostly 

 very similar habits and feed on similar food, in fact it is known that on some of the 

 different islands a good deal of this food consists actually of the very same species 

 of insects. Having a very varied dietary on each island, we may consider that the 

 food of each species is practically the same. Moreover, as some of the species thrive 

 in different areas, each on its own particular island, these areas having quite different 

 climates, vegetation, rainfall etc., it is clear that it is not these conditions that 

 necessarily affect the species. This is a very important point to remember in con- 

 sidering the effects of isolation. 



Again and again in insects we find a species inhabiting one island replaced on 

 several of the others by closely allied forms, so that we can feel sure these have been 



