INTRODUCTION Ixiii 



psittaced) and a second containing forms restricted to one, or very rarely found on 

 two adjoining islands. This latter group comprises most of the endemic Passerine 

 birds. Even the native crow and buzzard, birds of very great powers of flight, do 

 not occur except on the island of Hawaii. 



In insects one notices the same phenomena. In this group, speaking generally, 

 the more widespread forms are usually endowed with powers of flight. Even in 

 the Carabidae, where the vast majority of the species are known only from one island, 

 it is mostly the winged forms that one finds on more than one island, either unmodified, 

 or with species hardly different from one another (cf. Bembidium teres, pacifiaun and 

 molokaiense, the species of Co/pocaccits, Colpodiscus hicipetens). The winged species 

 of minute beetles of the genus Cis are many of them of very wide distribution, so 

 are many of the Lepidoptera. Flightless species are rarely widely distributed. Those 

 species of the Cossonid genus of beetles, Dj-yophthorus, that live in logs, and are 

 extremely tenacious of life, however, are often of wide range. But, as in the birds, 

 hosts of insects with admirable powers of flight are quite confined to one island. 

 The Achatinelline shells, so richly represented on Oahu, Maui, Molokai and Lanai 

 are very poorly represented on Hawaii, and are nearly unrepresented on Kauai, where 

 the great genus Achatinclla is altogether wantiny. 



These facts seem to me to show clearly that, with certain exceptions, it must be 

 very rarely that a species passes from island to island so as to become established, and 

 that when this does happen, the immigrant is likely to be isolated for a very long time. 



Since in many insects amply endowed with powers of flight, and in the majority 

 of flightless species, there are closely allied but distinct forms in different islands, one 

 may consider that stray examples of a species have only to become separated from 

 the mass of individuals of that species and kept isolated, in order to become in time 

 so modified as to form new species. Where we find an endemic species spread over 

 each or several of the islands, we may suppose either that in such cases the species 

 in question, owing to powers and range of flight, or to other special facilities for 

 distribution, is carried from island to island sufficiently often to prevent isolation, or 

 that, if isolated, sufficient time for change has not yet elapsed. I have elsewhere 

 referred to the fact that there is good evidence to believe that owing to the stability 

 of species, even a great change of environment and isolation cannot be supposed as 

 a rule to affect a species after a few or even a considerable number of generations. 

 That isolation is a most important fact is evident from comparison of the fauna of 

 the several islands. In the Hawaiian group it may be roughly said that isolation 

 is directly proportional to the distance between these islands. If we consider a 

 large, well-collected and much studied genus, such as that of the wasps {Odynems) 

 we find that the comparatively approximated islands of Lanai, Maui and Molokai 

 have many species in common, while Hawaii has few such species, Oahu still fewer, 

 and Kauai, the most remote island, none at all. 



