Ixiv FAUNA HAWAIIENSIS 



We may see forms on the different islands in various stages of becoming distinct 

 species, from the earliest stage, where merely the range of variation of a species is 

 different on two islands, to that where every individual is different, but the differences 

 are so slight as to be hardly specific, and finally to that where the separating characters 

 are too important to be considered racial or varietal, when we may feel fairly confident, 

 that even should a fresh immigration of the original species take place from the one 

 island to the other, interbreedino- would not follow. 



Modifications following change of environment or isolation are of course subject 

 to the action of natural selection, which may expedite the formation or mould the 

 character of specific distinctions, but even without any selection the original species 

 will be changed if isolated and isolated long enough. It is not improbable that the 

 plastic condition of the species in so many genera, and the extreme difficulty that 

 exists in limiting the species, is really due to the slackness or absence of the agencies, 

 by which natural selection works, the struggle for existence in the case of many of 

 the island creatures having been much less severe than in a more populous and varied 

 fauna. 



One might cite any number of cases to show the effects of geographical isolation 

 on specific characters in insects, but one or two simple ones are sufficient. The little 

 bee Nesoprosopis anthracina occurs on all the islands from Oahu to Hawaii. It is 

 a xerophilous species, frequenting the flowers of Sida, Vitex, Waltheria, Tribuliis etc. 

 as well as plants introduced by man. On Kauai only it does not occur, but is there 

 replaced by N. fiavifrons, very closely allied to it, but quite distinct, with the same 

 xerophilous habits, and frequenting the same food-plants. Another species, N. facilis, 

 also found on all the islands but Kauai, is there replaced by an extremely closely 

 allied form A', chlorostida with similar habits. This case differs from the preceding 

 in that both these bees on their respective islands are wide-ranging, and able to 

 thrive in localities very diverse in climate and conditions. They range from the 

 coast to a height of fully 4000 ft. in mountain forests, and yet do not exhibit notable 

 variation under these diverse conditions. 



In cases where flightless and sluggish insects are found widely spread throughout 

 the islands, when one would naturally expect modification of specific characters to have 

 taken place on different islands, a careful study of life and habits will probably generally 

 show reasons for the suspicion that isolation is not complete. For instance we are 

 surprised to find a small, flightless and sluggish beetle like Proterhinus deceptor on 

 all the islands, little or not at all changed, but we search in vain for distinctions 

 between individuals taken on the various islands. Some variation there may be, but 

 this is no greater between examples from different islands than between others taken 

 on one island. In 1900, and subsequently, I paid some special attention to this case. 

 It was found that this small beetle breeds in profusion in dry regions below any 

 existing forest, in scattered trees, though it also occurs at high elevations in the 



