The ultimate result of centuries on centuries of the restlessness of individuals is seen in the facts of geographical distribution. Only in the most general way can the history of any species be traced; but could we know it all, it would be as long and as eventful a story as the history of the colonization and settlement of North America by immigrants from Europe. But 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 a struggle of life and death; for each fish is a cannibal, and to each species each member of every other species is an alien and a savage. FOOTNOTES: [100] Except possibly the Sacramento. [101] Unless the fauna of certain cave streams in the United States and Cuba be regarded as forming an exception. [102] For example, Elk River, Duck River, etc. [103] There are three species of darters (_Cottogaster copelandi_ Jordan, _Hadropterus evides_ Jordan and Copeland, _Hadropterus scierus_ Swain) which are now known only from the Ozark region or beyond and from the uplands of Indiana, not yet having been found at any point between Indiana and Missouri. These constitute perhaps isolated colonies, now separated from the parent stock in Arkansas by the prairie districts of Illinois, a region at present uninhabitable for these fishes. But the non-occurrence of these species over the intervening areas needs confirmation, as do most similar cases of anomalous distribution. [104] Thus, _Dorosoma cepedianum_ Le Sueur and _Pomolobus chrysochloris_ Rafinesque have found their way into Lake Michigan through canals. [105] _Oncorhynchus tschawytscha_ Walbaum. [106] _Oncorhynchus nerka_ Walbaum. [107] "In this isolated region of North America, in this zoological island of New England, as we may call it, we find neither Lepidosteus, nor Amia, nor Polyodon, nor Amblodon (_Aplodinotus_), nor Grystes (_Micropterus_), nor Centrarchus, nor Pomoxis, nor Ambloplites, nor Calliurus (_Chænobryttus_), nor Carpiodes, nor Hyodon, nor indeed any of the characteristic forms of North American fishes so common everywhere else, with the exception of two Pomotis (_Lepomis_), one Boleosoma, and a few Catostomus."--AGASSIZ, _Amer. Journ. Sci. Arts_, 1854. [108] _Catostomus_, _Pantosteus_, _Chasmistes_. [109] _Gila_, _Ptychocheilus_, etc. [110] _Salmo clarkii_ and its varieties. [111] Genera _Notropis_, _Chrosomus_, etc. [112] As the fresh-water surf-fish (_Hysterocarpus traski_) and the species of salmon. [113] _Salmo clarki_ Richardson. [114] _Coregonus williamsoni_ Girard. [115] _Salvelinus malma_ (Walbaum). [116] _Thymallus tricolor_ Cope. [117] _Salvelinus fontinalis_ Mitchill. [118] _Notropis rubricroceus_ Cope, _Rhinichthys atronasus_ Mitchill, etc.