Unfortunately, the only attempt to study the mam- 

 malian life zones of Pennsylvania was made twenty- 

 five years ago (Rhoads 1903) and, undoubtedly, the 

 distribution is somewhat altered at the present time. 

 It is well known that some animals are fairly well dis- 

 tributed over the state, while others are confined to 

 comparatively narrow limits. There are numerous 

 factors which explain both the general and specific lo- 

 calities of various mammalian forms. Undoubtedly, 

 the mountains have previously proved an effective bar- 

 rier to many forms, but the opening of highways has 

 altered their effectiveness to some extent. On the other 

 hand, the mountains provide a more suitable set of con- 

 ditions for some animals that are to be found only with- 

 in their confines. The great variety of conditions that 

 obtain within the Commonwealth yield an interesting 

 fauna. 



The foregoing sketchy account of some of the fac- 

 tors that contribute to the diversification and distribu- 

 tion of animal groups is given only to indicate the 

 breadth of Mammalian study. It is hoped that these 

 scattered suggestions and illustrations will stimulate the 

 intellectual curiosity of the reader and arouse in him an 

 aggressive interest. Further details would add too 

 much volume to this treatise and thus destroy the pur- 

 pose of the writer. The Classified Bibliography con- 

 tains a sufficient number of both general and specific 

 works for ordinary purposes. 



The Hair of Mammals 



With a few exceptions such as Whales, Dolphins, 

 etc., the mammals are covered with a coating of hair 

 of varying length and thickness according to the spec- 



-*>C 23 >*- 



