2o6 Flashlights on Nature 



of oceanic islands (for I need hardly say I set 

 aside mere limnan a<4encies) consists almost en- 

 tirely of birds blown across from the nearest con- 

 tinent, and their descendants ; of reptiles, whose 

 small e^54s can be transported in logs of wood 

 or broken trees by ocean currents ; of snails and 

 insects, whose still tinier spawn can be conveyed 

 for long distances by a thousand chances ; and of 

 such trees, herbs, or ferns as have very light seeds 

 or spores, easilv whirled by storms (like thistle- 

 down), or else nuts or hard fruits which may be 

 wafted by sea-streams without damage to the 

 embryo. For the most part, also, the plants and 

 animals of oceanic islands resemble more or less 

 closely (with locally induced differences) those of 

 the nearest continent, or those of the land from 

 which the prevailing winds blow towards them, 

 or those of the country whence currents run most 

 direct to the particular island. They are waifs 

 and strays, stranded there by accident, and often 

 giving rise in prt)cess of time to special local 

 varieties or species. 



Now, it is much the same with isolated ponds. 

 They acquire their first inhabitants by a series of 

 small accidents. Perhaps some water-bird from a 

 neighbouring lake or river alights on the sticky 

 mud of the bank, and brings casually on his 

 webbed feet a few clinging eggs of dace or chub, 

 a few fragments of the spawn of pond-snails or 

 water-beetles. Paddling about on the brink, lie 

 rubs these off by mere chance on the mud, where 

 they hatch in time into the first colonists of the 



