5o6 POPULAR SCIENCE MONTHLY. 



strong as to easily sustain the weight of a man. The walls are 

 generally about six inches in thickness and are very difficult to 

 pull to pieces. Within is a single circular chamber with a shelf 

 or floor of mud, sticks, leaves, and grass, ingeniously supported 

 on coarse sticks stuck endwise into the mud after the manner of 

 piles. In the center of this floor is an opening, from which six 

 or eight diverging paths lead to the open water without, so that 

 the little artisan has many avenues of escape in case of danger. 

 These houses are often repaired and used for several winters in 

 succession, but are vacated on the approach of spring. During 

 the summer the muskrat is, in the main, a herbivorous animal, 

 but in the winter necessity develops its carnivorous propensities 

 and it feeds then mainly upon the mussels and crayfish which it 

 can dig from the bottom of the pond or stream in which its house 

 is built. 



The bats pass the winter in caves, the attics of houses and 

 barns, or in hollow trees, hanging downward by their hind claws, 

 eating nothing and moving not. All the carnivora, or flesh-eaters, 

 as the mink, skunk, opossum, fox, and wolf, are in winter active 

 and voracious, needing much food to supply the necessary animal 

 heat of the body. Hence they are then much more bold than in 

 summer, and the hen yard or sheep pen of the farmer is too fre- 

 quently called upon to supply this extra demand. 



But of all our animals it seems to us the birds have solved the 

 winter problem .best. Possessing an enduring power of flight and 

 a knowledge of a southern sunny sky, beneath which food is 

 plentiful, they alone of the living forms about us have little fear 

 of the coming of the frost. True, forty or more species remain in 

 each of the Northern States during the cold season,' but they are 

 hardy birds which feed mainly on seeds, as the snow bird and 

 song sparrow ; on flesh, as the hawks and crows ; or on burrow- 

 ing insects, as the nuthatches and woodpeckers. And no winter 

 day is too dull and dreary, no sky too leaden and cheerless, no 

 north wind too harsh and biting for them to be on the lookout 

 for food. 



Such are some of the solutions to the problem of life in winter 

 which the plants and animals about us have worked out; such 

 some of the forms which they undergo, the places which they 

 inhabit. 



To the thinking mind a knowledge of these solutions but be- 

 gets other and greater problems, such as how can a living thing 

 be frozen solid for weeks and yet retain vitality enough to fully 

 recover ? How can a warm-blooded animal sleep for months 

 without partaking of food or drink ? And, greater than either. 

 What is that which we call life ? 



I hold in my hand two objects, similar in size, color, organs. 



