STRIICTIJRT^ OK MAMMAfiS. 



421 



dacks, and Rhoads' Mammals of Pennsylvania and New Jersey, 

 have been relied on for much information. The numerous mono- 

 graphs published by the Department of Agriculture and the Na- 

 tional Museum have also been invaluable, and most of the figures 

 of skulls and teeth have been borrowed from them. The nomen- 

 clature is that of Miller and Rehn 's List of North American Mam- 

 mals, with a few corrections, made necessary by discoveries since 

 its publication. The keys are modified from Miller's Key to the 

 Land Mammals of Northeastern North America. A full list of the 

 works consulted in the preparation of the paper will be found in 

 the bibliography. 



Much information has been received from men in all parts of 

 the State whose names it is not possible to enumerate. But special 

 thanks are due to Mr. E. J. Chansler, of Bicknell, for notes and 

 information very carefully collected by him in that locality during 

 many years; to Prof. Van Gorder for similar notes from Noble 

 County; to Dr. C. H. Eigenmann, of Indiana University, for 

 assistance in many ways, and to Prof. W. S. Blatchley for informa- 

 tion and assistance, and for the assistance from his Department 

 which has made possible two field trips. 



THE CLASS MAMMALIA. 



STRUCTURE AND ZOOLOGICAL POSITION. 



The class Mammalia includes such diverse creatures as whales, 

 bats and man, as well as most of the common four-footed animals. 

 Unfortunately the word "mammal" has never come into general 

 use, and there is no other word in the English language that is an 

 exact equivalent. Quadruped, which is sometimes used, includes 

 lizards, frogs and other animals which are not members of the 

 cla^, and does not include whales, man and bats, which are. 



A mammal has been very simply defined as a "warm blooded, 

 air-breathing animal that suckles its young." In addition to these 

 characters, land mammals are always covered with hair and never 

 with scales; there is a complete double circulation of the blood 

 and a four-chambered heart ; the skull articulates with the verte- 

 bral column by means of two rounded surfaces (occipital condyles) 

 instead of one, as in birds and reptiles; there are teeth in both 

 jaws, except in a few species in which they have degenerated; 

 there is a corpus callosum uniting the two hemispheres of the brain ; 

 a complete diaphram- separates the thorax from the abdomen ; and, 

 most important of all, the fertilized ovum is retained in the body 



