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is great vicissitude of climate the smaller animals are 

 supplied with natural clothing adapted to the seasons, and 

 instincts guiding them to seek and prepare for themselves 

 proper shelter against the cold. In the second place, age 

 modifies the power which the animal possesses of generating 

 heat. Among mammalia and birds, the young come into 

 the world from the womb or egg at different degrees 

 of development. In both classes, two divisions are 

 formed from this circumstance, well distinguished by ex 

 ternal characters. In mammalia, the young are born with 

 their eyes closed or opened. In birds, the young are 

 hatched without or with feathers. These external charac- 

 ters correspond with, in the mammals with closed eyes, and 

 birds without feathers, a more incomplete development of 

 the internal organs. Animals in these circumstances require 

 a more close attention from their mothers, to enable them 

 to preserve the temperature necessary for health, and if they 

 be removed from them, their temperature gradually sinks to 

 a limit which is that of the external atmosphere. In the 

 young animals which are born with their eyes open, and 

 with feathers or down, the temperature, when they are 

 removed from their mother, sinks a few degrees, and is then 

 maintained at a fixed point by the internal heat- generating 

 powers of the animal. Edwards found that the temperature 

 of a puppy twenty-four hours old, separated from its 

 mother, sunk, in an atmosphere which was at 55°, in the 

 course of four hours, from 98° 36, to 64°.43 ; and in four 

 younger puppies, it sunk, in thirteen hours, from the same 

 point to a temperature only 1°.8 above that of the atmos- 

 phere. In the guinea pig, goat, and other animals, the 

 temperature of the separated animal only sank a few 

 decrees below that of the mother, under the same circum- 

 stances, and remained stationary at this point. Similar 

 results were observed in the temperature of the bird 

 hatched unfledged. In these last it might be said, that 



