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 firs^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 



