net nothing large or small ever comes amiss ; and wherever I 

 go, I find cases like this. 



We do not know all the fishes of America yet, nor all those 

 well that we know by sight ; still this knowledge will come 

 with time and patience, and to procure it is a comparatively 

 easy task. It is also easy to ascertain the more common 

 inhabitants of any given stream. It is difficult, however, to 

 obtain negative results which are really results. You cannot 

 often say that a species does not live in a certain stream. You 

 can only affirm that you have not yet found it there, and you 

 can rarely fish in any stream so long that you can find nothing 

 that you have not taken before. Still more difficult is it to 

 gather the results of scattered observations into general state- 

 ments regarding the distribution of fishes. The facts may be 

 so few as to be misleading, or so numerous as to be confusing ; 

 and the few writers who have taken up this subject in detail 

 have found both these difficulties to be serious. Whatever 

 general propositions we may maintain must be stated with the 

 modifying clause of "other things being equal"; and other 

 things are never quite equal. 



Still less satisfactory is our attempt to investigate the causes 

 on which our partial generalizations depend — to attempt to 

 break to pieces the " other things being equal " which baffle 

 us in our search for general laws. 



We now recognize about six hundred species of fishes as 

 found in the fresh waters of North America, north of the Tropic 

 of Cancer, these representing thirty-four of the natural families. 

 As to their habits, we can divide these species rather roughly 

 into the four categories proposed by Professor Cope, or, as we 

 may call them — 



(i) Lowland fishes; as the bow-fin, pirate perch, large- 

 mouthed black bass, sunfishes and some catfishes. 



(2) Channel fishes ; as the channel catfish, the moon-eye, 

 gar-pike, buffalo-fishes and drum. 



(3) Upland fishes ; as many of the darters, shiners and 

 suckers, and the small-mouthed black bass. 



(4) Mountain fishes ; as the brook trout, and many of the 

 darters and minnows. 



