LIFE'S BORDERLANDS 



No picture is complete without its frame. Let us therefore 

 frame our presentation of the animal life upon the earth with 

 a consideration of life's borderlands, an outline of the extreme 

 limits within which animal life exists. 



Suppose someone should say that there were millions of 

 animals now living which had never experienced a temperature 

 as high as that of the cakes of ice in the ordinary refrigerator. 

 Such a statement at first sight appears incredible, and yet it is 

 perfectly true. 



In the winter when the ground and ponds are frozen the 

 plants cease to grow and become dormant. The turtles, snakes, 

 lizards and frogs, the butterflies, bees, ants and other insects, 

 the snails and the earth-worms, all pass into the long sleep 

 known as hibernation, and the only active living things about 

 us are the winter birds and mammals. All birds are perpetually 

 active, and all of them that cannot find sufficient food or stand 

 the cold go south; but some mammals, like the bears, hide 

 away and sleep throughout the winter, while many others, like 

 the squirrels and the field mice, sleep most of the time, ap- 

 pearing at intervals on warm and sunny days. 



It is evident, then, that on land the activity of most living 

 things comes to rest at a temperature of about 40°, or at the 

 lowest at the freezing point of water, a substance essential for 

 the support of life but one which few creatures can use in 

 the form of ice because of the great expenditure of energy 

 necessary to reduce it to its liquid condition, in which con- 

 dition alone can it be utilized. 



In certain portions of the sea, deep down where the heat 

 from the sun never penetrates and where it is darker than the 

 darkest night, there is perpetual winter with an absolutely 



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