viii MAMMALS OF AMERICA 



more highly developed heart of the Mammal. The diaphragm, a typically mammalian 

 structure, is a thin muscular wall separating the cavity containing the lungs and heart from 

 the other internal organs. This separation results in a better opportunity for the function- 

 ing of the various organs, and is a development upward. Finally, the brain of the Mammal 

 is marvelously developed and is far in advance of that of members of other classes. The 

 increase is in both quantity and quality, in volume proportionally to the weight of the animal, 

 and in the development of the higher centers and convolutions. 



SUBDIVISIONS OF M.\MMALS 



Now with a better idea of what a Mammal, any Mammal, is, the next step is to see 

 how its different members differ from one another. Students have divided the class Mam- 

 malia into two large divisions, based upon the degree of development; the least developed 

 belong to the Protothcria, or ancient Mammals, while the more highly developed forms belong 

 to the Eutheria, or modern Mammals. The Prototheria are represented today by only two 

 types, the Duckbill Platypus, or Ornithorhynchus, and the Spiny Anteater, or Echidna, 

 both very strange-appearing animals to be found only in Australia and neighboring 

 islands. They lay eggs, but otherwise more closely resemble true Mammals than any other 

 class, although they are connecting links with the lower animals. We are concerned only 

 with the Eutheria, since all the North American Mammals belong to this subdivision. 



Because of the wide diversity of types it was early found that, in order to make anything 

 like a close study of Mammals, a careful classification must be arranged. This classification 

 has been built up on names formed on Latin and Cireek roots. The reason for this becomes 

 evident when one learns the difficulty of trying to do anything with the so-called common 

 names of Mammals. For example, the English-speaking settlers of North America brought 

 over Old World names with which they were familiar, and applied them to New World 

 Mammals with which they were not familiar. The result is that such animals as the 

 American Elk and Buffalo have received these names from a fancied identity with 

 Old World animals, while as a matter of fact these names are misleading and should apply 

 only to the much different animals on the other side of the Atlantic. The common name 

 of " Gopher " is variously used in different localities for Ground Squirrels, Chipmunks, and 

 Pocket Gophers, and consequently means nothing in an exact treatise, whereas the scientific 

 name of an animal means the same the world over. Thus the classification which at first 

 appears to be cumbersome and unnecessary is seen to be absolutely essential to a clear 

 understanding of the Mammals from widely separated localities. 



HISTORY OF CLASSIFICATION 



Attempts at classification were made in very early times. One of the earliest of 

 these is contained in Leviticus XL where Mammals are classified into those that divide the 

 hoof and chew the cud, and the Camel, the Cony and the Hare are enumerated among others. 

 The early Assyrians (about 668 B. C.) made an evident attempt to classify into divisions 

 like our modern families and genera, for they put the Dog, Lion, and Wolf into one category 

 and the Ox, Sheep and Goat into another. The history of classification begins with Aristotle 

 (B. C. 384-322) who was a good observer and compiler, but who has commonly been credited 

 with ideas more advanced than were actually the case. He uses the words genus and species. 

 Following Aristotle comes a long lapse of time wherein nothing of great importance was added 

 to the classification of animal life. Gesner(i 551-1558) and Wotton(i552) are the landmarks 

 for the i6th century. Ray (1693) began with the method of the Greeks, but left a method 

 that marks most decided advances. His tables of classification chose characters of more 

 fundamental value, and he discarded the habitat or home of the animal as a means of classi- 

 fication. Earlier writers made up groups into Terrestrial, Aquatic, and Amphibious, regard- 

 less of the true relationships of the animals. For example, the Seal and the Frog are both 



