16 MY ISLANDS. 



in the matter of cosmopolitan dispersion ; for while it 

 was quite impossible for rats, mice, or squirrels to cross 

 the intervening belt of three hundred leagues of sea, 

 their little winged relation, the flitter-mouse, made the 

 journey across quite safely on his own leathery vans, and 

 with no greater difficulty than a swallow or a wood- 

 pigeon. 



The insects of my archipelago tell very much the 

 same story as the birds and the plants. Here, too, 

 winged species have stood at a great advantage. To be 

 sure, the earliest butterflies and bees that arrived in the 

 fern-clad period were starved for want of honey ; but as 

 soon as the valleys began to be thickly tangled with 

 composites, harebells, and sweet-scented myrtle bushes, 

 these nectar-eating insects established themselves 

 successfully, and kept their breed true by occasional 

 crosses with fresh arrivals blown to sea afterwards. 

 The development of the beetles I watched with far 

 greater interest, as they assumed fresh forms much more 

 rapidly under their new conditions of restricted food and 

 limited enemies. Many kinds I observed which came 

 originally from Europe, sometimes in the larval state, 

 sometimes in the egg, and sometimes flying as full-grown 

 insects before the blast of the angry tempest. Several 

 of these changed their features rapidly after their arrival 

 in the islands, producing at first divergent varieties, and 

 finally, by dint of selection, acting in various ways, 

 through climate, food, or enemies, on these nascent 

 forms, evolving into stable and well-adapted species. 

 But I noticed three cases where bits of driftwood thrown 

 up from South America on the western coasts contained 



