CHAPTER IV 

 THE FRESH WATERS 



Variety of the Fresh Waters Similar Animals in widely sep- 

 arated Places From Salt Water to Fresh Origin of 

 Fresh-water Animals Circulation of Matter in the Fresh 

 Waters The Web of Life in the Fresh Waters The Dan- 

 ger of Drought The Danger of Frost The Danger of 

 Flood Parental Care among Fresh-water Animals The 

 Story of the Eel The Story of the Salmon The Story of 

 the Lamprey Water Insects The Story of the Fresh- 

 water Spider. 



THE fresh waters do not occupy even a 

 hundredth part of the earth's surface 

 1,800,000 square miles out of the 197,000,000, 

 which form the total. But the haunt makes 

 up for its relatively small size by its great 

 variety. 



VARIETY OF THE FRESH WATERS 



There are lakes so vast that their depths may 



be as cold, and dark, and plantless as those of 



the sea itself. Lake Baikal in Asia has a depth 



of 760 fathoms, with an additional atmosphere 



136 



