322 GENERAL ZOOLOGY 



become fetid with decaying vegetation, and during the time 

 it breathes air." The African and South American species 

 " bury themselves in mud during the dry season, a necessary 

 precaution, since they inhabit swamps which dry up." 



Economic Importance of Fishes. The value to a people of 

 an abundant and cheap fish-supply cannot be overestimated. 

 Recognizing its importance, the United States government 

 has long maintained a Commission of Fish and Fisheries 

 (the name of which has been changed recently to Bureau of 

 Fisheries), which has been active along both practical and 

 scientific lines. Among the subjects which are considered 

 by the bureau are the resources of our inland and coastal 

 waters, the geographical distribution of the economically im- 

 portant fishes inhabiting them, and the study of the natural 

 history of fishes, their enemies, diseases, and the remedies 

 therefor. It has also made statistical researches into the con- 

 dition and commercial value of the fishing industries of the 

 United States, and the methods employed in these industries ; 

 and, perhaps the most important of all, it has carried on the 

 artificial propagation and distribution of valuable species. 

 Thus, during the year ending June 30, 1901, 1,173,833,400 

 fishes and eggs were distributed to different parts of the 

 United States, the principal species being shad, salmon, lake- 

 trout, whitefish, pike, perch, lake-herring, cod, and flatfish. 

 In this way many bodies of water have been restocked after 

 indiscriminate destruction. 



Geographical Distribution of Fishes. A simple and seem- 

 ingly natural classification of fishes, as regards their hab- 

 itat, is a division into fresh-water and marine forms ; and this 

 will serve our purpose if it be remembered that there has 

 been much interchange of species between the two media. 

 In general, the truly fresh-water species of the world vary 

 in connection with the great faunal regions mentioned on 

 page 94. In the North American and Eurasian realms some 



