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CHAPTER XIV 

 THE GEOGRAPHICx\L DISTRIBUTION OF FISHES 



OOGEOGRAPHY.— Under the head of distribution we 

 consider the facts of the actual location of species 

 of organisms on the surface of the earth and the 

 laws by whicli their location is governed. This constitutes 

 the subject-matter of the science of zoogeograpliy. In physical 

 geography we maj' prepare maps of the earth or of any part of 

 it, these bringing to prominence the physical features of its 

 surface. Such maps show here a sea, there a plateau, here a 

 mountain chain, there a desert, a prairie, a peninsula, or an 

 island. In political geography the maps show their physical 

 features of the earth as related to the people who inhabit 

 them and the states or powers which receive or claim their 

 allegiance. In zoogeography the realms of the earth are con- 

 sidered in relation to the species or tribes of animals which 

 inhabit them. Thus series of maps could be drawn representing 

 those parts of North America in which catfishes or trout or 

 sunfishes are found in the streams. In like manner the distri- 

 bution of any particular fish as the muskallonge or the yellow 

 perch could be shown on the map. The details of such a map 

 are very instructive, and their consideration at once raises a 

 series of questions as to the cause behind each fact. In science 

 it must be supposed that no fact is arbitrary or meaningless. 

 In the case of fishes the details of the method of diffusion of 

 species afford matters of deep interest. These are considered 

 in a subsequent chapter. 



The dispersion of animals may be described as a matter of 

 space and time, the movement being continuous but modified 

 by barriers and other codnitions of environment. The ten- 

 dency of recent studies in zoogeography has been to consider 



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