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Each of the 600 species we now know is making every year 

 inroads on territory occupied by other species. If these colo- 

 nies are able to hold their own in the struggle for possession, 

 they will multiply in the new conditions and the range of the 

 species will become widened. If the surroundings are differ- 

 ent new species or varieties may be formed in time and these 

 new forms may again invade the territory of the parent species. 

 Again colony after colony of species after species may be 

 destroyed by other species or by uncongenial surroundings. 



The ultimate result of centuries on centuries of the restless- 

 ness of individuals is seen in the facts of geographical distribu- 

 tion. Only in the most general way can the history of any 

 species be traced. Could we know it all, it would be as long 

 and eventful a story as the history of the colonization and set- 

 tlement of North America by immigrants from Europe. 



By the fishes each river in America has been a hundred 

 times discovered ; its colonization a hundred times attempted. 

 In these efforts there is no co-operation. Every individual is 

 for himself, every struggle is a struggle of life and death. Each 

 fish is a cannibal, and to each species each member of every 

 other species is an alien and a savage. Now all this hasw a 

 practical side to it, although the practical side has been as yet 

 little developed. 



A leading feature of the work of the Fish Commissions 

 must be to help the fishes over the barriers, to assist nature in 

 the direction of colonizing streams and lakes with fishes which 

 are good to eat, to the exclusion of the kinds of which man can 

 make no use. 



This help may be given by the introduction of vigorous 

 kinds of fishes into waters into which they had been unable to 

 find an entrance before. The work judiciously done may be of 

 the greatest value to the people of our country. Numerous as 

 are the food fishes of the Mississippi valley, it must be confessed 

 that the rank of the great bulk of them is not high. Our rivers 

 ought to raise something better than suckers, paddle-fish, drum 

 and buffaloes. To bring in better fishes with success, it is nec- 

 essary for us to know something of the habits and necessities of 

 the species in question, and also something definite as to the 



