A FROZEN WORLD 207 



new water-world. Perhaps, again, a heron drops 

 a half-eaten fish into the water a fish which is 

 dead itself, but has adhering to its scales or gills a 

 few small fresh-water crustaceans and mollusks. 

 Perhaps a flood brings a minnow or two and a 

 weed or two from a neighbouring stream; perhaps 

 a wandering frog trails a seed on his feet frcm 

 one pool to another. By a series of such acci- 

 dents, each trivial in itself, an isolated pond 

 acquires its inhabitants ; and you will therefore 

 often find two ponds close beside one another 

 (but not connected by a stream), the plants and 

 animals of which are nevertheless quite different. 



Now, the pond in summer is one thing ; the 

 pond in winter is quite another. For just reflect 

 what winter means to this little, isolated, self-con- 

 tained community ! The surface freezes over, and 

 life in the mimic lake is all but suspended. Not 

 an animal in it can rise to the top to breathe ; not 

 a particle of fresh oxygen can penetrate to the 

 bottom. Under such circumstances, when you 

 come to think of it, you might almost suppose 

 life in the pond must cease altogether. But nature 

 knows better. With her infinite cleverness, her 

 infinite variety of resource, of adaptation to cir- 

 cumstances, she has invented a series of extra- 

 ordinary devices for allowing all the plants and 

 animals of a pond to retire in late autumn to its 

 unfrozen depths, and there live a dormant exist- 

 ence till summer comes again. Taking them in 

 the mass, we may say that the population sink 

 down to the bottom in November or December, 



