431 



fauna is the fact that nearly all groups are inhabitants of dead 

 wood and debris of the kind that sometimes drifts about the 

 oceans, or if not of that type are usually strong in flight. 

 There are no native leaf-eating beetles or grasshoppers or simi- 

 lar insects. The beetles are nearly all wood-borers or ground 

 beetles which commonly hide away under bark. Nearly all the 

 Hymenoptera are borers or forms which nest in logs, etc. Dip- 

 tera are represented mostly by debris inhabiting forms, while 

 of the Lepidoptera we have no native butterflies except one 

 comparatively recent immigrant, but a considerable number of 

 moths some of which are strong in flight and others pupate 

 under bark or in similar situations. 



The conclusion to be drawn from these facts is that these 

 Islands have been in existence for a very great length of time 

 — long enough for many species to have originated here from 

 a few ancestors — a conclusion which is also supported by 

 geological evidence which points to the existence of the land 

 mass as far back as the Paleozoic. Another conclusion to be 

 drawn from our data is that the islands have always been iso- 

 lated and never a part of a continental land mass, hence re- 

 ceiving no migrations of animals overland but only by long 

 and very precarious voyages over the ocean in logs and floating 

 debris, and perhaps by flight and carriage by winds. From the 

 very small number of ancestral types represented by the en- 

 demic species it would appear that only very rarely did insects 

 and shells succeed in establishing themselves in these Islands. 



The presence here of some very delicate insects is more 

 difficult to explain. They do not inhabit logs nor debris al- 

 though some are gall makers, and their span of life is very 

 short, especially short in the absence of living foliage to fur- 

 nish them food. Certain homopterous insects, the leaf hoppers 

 and jumping plant lice, are good examples of this type. It 

 is not possible to explain their entrance here by way of a land 

 bridge now disappeared, for if there had been such a bridge 

 beyond doubt more than the meagre few would have become 

 established here. There remains, then, only the ae'encv of 



