INTRODUCTION. 11 



Geographical Distribution. Animals are not arbitrarily 

 scattered over the earth's surface, but form assemblages of 

 species which people any given spot or country. Such an 

 assemblage of animals inhabiting a given place or area is 

 called a fauna. Thus we may speak of the fauna of New 

 York, or of the United States, or of North America. The 

 animals of the arctic region belong to the arctic fauna; 

 those of the tropics constitute the tropical fauna. We 

 may also speak of the fauna of the land or of the ocean. 



Where the physical geography i.e., the contour of the 

 surface, the plains, valleys, and hills is similar in charac- 

 ter and the climate the same, the fauna is nmch the same; 

 but when these characteristics of soil and climate change, 

 as in passing from lowlands to highlands, or from south to 

 north, the assemblage of animals will be found to change in 

 a corresponding ratio. And as there are no definite limits 

 to any large area of the earth's surface, the physical fea- 

 tures of one area merging insensibly, as a rule, into adjoin- 

 ing districts, so adjoining faunae merge into one another, 

 and a certain proportion of the species may range through 

 two or more faunal areas. 



At almost any point in temperate North America the 

 fauna is found to consist of three elements i.e., mainly a 

 temperate, with a certain percentage of boreal or subarctic, 

 and of southern or semi-tropical forms; and if the point be 

 situated near some lofty range of mountains, a fourth ele- 

 ment i.e., a purely arctic or alpine feature is superadded. 



Marine animals are also assorted into faunas, which are 

 nearly as well marked as land-faunae. Below a depth of a 

 thousand feet, where the temperature is from 32 to 40 F., 

 deep-sea animals occur, forming the abyssal fauna. 



