Ixx FAUNA HAWAIIENSIS 



species. The pairing of the AchatinelHdae seems to have been very little observed,, 

 and I myself have only three times seen these animals in copula. Two of these 

 cases were pairings between extreme varieties of Achatinella redfieldi, and in each 

 case the individuals in copula were of exactly the same colour-form, one pair being 

 the albino variety. The other case was that of another Molokai species, A. macrodon, 

 the individuals being identical in colour. No importance can be attached to these 

 few instances. 



Reviewing the whole fauna, the widespread effect of segregation in species- 

 formation becomes evident, whether the segregation is brought about by geographical 

 isolation, or by change of food or habits. In the case of very sluggish animals, like 

 the Mollusca, a mountain valley or ridge may prove an . effectual isolating barrier, 

 or in fully-winged insects a narrow interisland channel. Exactly how far modification 

 is due to the direct effect of food or difference of habits and how far to the mere fact 

 of segregation is not known, but it appears to me that segregation is the most 

 important. The extraordinary series of well-defined but closely allied species of 

 Homopterous insects, each attached to its own special food-plant, are very interesting 

 in this connection. Considering the fact that individuals frequenting the same food- 

 plant, but geographically isolated, are so often modified as to form distinct species 

 or races, isolation appears the most important factor. The little Drepanid bird, 

 Himatione sanguinca, of vagrant habits and inhabiting all kinds of stations throughout 

 the main group of islands, on remote Laysan is replaced by the allied H. freethi. 

 A few individuals of the former, chancing to reach that remote island, would probably 

 remain isolated for ages, and this is probably what has happened in the past, the 

 modified H. freethi being the result. 



Summary of general part of the Introduction. 



The Hawaiian fauna cannot be said to belong to any of the great faunistic regions 

 of the globe, it contains most important elements derived from the Oriental region, 

 from the Australian and from the Neotropical or at least from the warmer parts of 

 America, and it cannot be considered as even belonging chiefly to any one of these 

 regions. On present information it is decidedly not Polynesian, but a proper study 

 of the Samoan and other groups may show greater affinities with these than is apparent 

 to-day. The Fijian fauna is extremely unlike the Hawaiian in nearly every respect. 

 The small islands (Christmas, Fanning, etc.) that lie nearly midway between Hawaii 

 and the Samoan group are in sad need of exploration, as also is the latter. Many 

 of the most important components of the fauna are so remarkably isolated (e.g. the 

 Achatinellid Mollusca and many groups of insects richly represented in species) that we 

 cannot even conjecture whence they have been derived. Even the family Drepanididae 

 in the birds has somewhat doubtful affinities, as also has the genus of thrushes Phaeornis. 



