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. 
HE 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 
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