12 VERTEBRATE ANIMALS OF THE UNITED STATES 



eastern and central northern United States, the higher Alleghanies and 

 the mountains of the West. 



The Austral Region comprises the greater part of the United States, 

 and is composed of the Transition, Upper Austral and Lower Austral 

 zones, each transcontinental in extent, the limits of which may be 

 seen by reference to the frontispiece. The life conditions of the 

 eastern and western portions of these three zones are greatly affected 

 by the differences in the precipitation of moisture in them. The one- 

 hundredth meridian represents the approximate boundary between the 

 w^ell-watered prairies and the arid Great Plains, to the eastward of which 

 the annual rain-fall is greater than 25 inches and to the westward it is 

 less than that amount, except on the Pacific coast. The eastern 

 divisions of the three Austral zones are also called the Alleghanian, 

 Carolinian and Austroriparian, respectively, and the two most 

 southerly western divisions are also called the Upper So nor an and 

 Lower Sonoran. 



The Tropical Region comprises the southern portion of the conti- 

 nent and occupies only a small part of this country, being limited to 

 the southern end of Florida, south of Lake Worth, and perhaps the 

 valley of the lower Colorado. 



History.- — The first person in modern times to unite the different 

 classes of vertebrates in a single phylum was the French naturalist 

 Lamarck, who, near the beginning of the 19th century, divided all 

 animals into the two groups of those with vertebrae and those without. 

 Aristotle, in his time, pointed to the same fundamental subdivision of 

 the animal kingdom when he contrasted the several classes possessing 

 red blood with those apparently without blood, their blood being color- 

 less. The Swedish naturahst Linnaeus, the founder of the modern 

 system of classifying animals and plants, who lived in the generation 

 immediately preceding Lamarck, did not take notice of the interrela- 

 tionship of the classes of vertebrates notwithstanding the example of 

 Aristotle, but gave each of these classes equal rank in his system with 

 the invertebrate groups. Cuvier, who was a younger contemporary and 

 fellow-countryman of Lamarck, adopted the term Vertehrata introduced 

 by him as one of the four fundamental types into which he divided the 

 Animal Kingdom, and the group maintained this rank in the zoological 

 system of classification until about the seventh decade of the last 

 century. At that time the epoch-making researches of Kowalevsky 

 and others having shown the relationship of vertebrates with ascidians, 

 Amphioxus and Balanoglossus, a new phylum was formed, first by the 

 German zoologist Haeckel, to include these groups, which received the 



