Introduction 



be venomous in the colder waters of our northern coasts. They 

 are by no means food-fishes, and are mentioned here only that 

 they may be avoided. 



Setting aside, then, all these, the small, the lean, the coarse, 

 the poisonous, the rank, the rare, and the inhabitants of the oceanic 

 abysses, we still have left a royal assemblage of food and game- 

 fishes, and all these are treated in the present volume. Of these, 

 the total number of species is about one thousand, fully one-third 

 of all the food and game-fishes of the world, or nearly one-third 

 of all the fishes of whatever kind known from American waters. 

 A few which may be called unimportant are important to some- 

 body and are therefore included, even though scarcely mentioned 

 in any other work. Thus the great catfish of the Rio de las Balsas 

 in Mexico (1st I an' us balsamis) is important to the natives of 

 Morelos, though unknown to every one else. On the other hand, 

 we may have omitted species important to somebody because they 

 do not concern the reader and have never interested us. The line 

 between those we include and those we pass unmentioned is often 

 a very narrow one which might easily be shifted either way. 



This book is a treatise on a branch of Ichthyology, and 

 Ichthyology is the science of fishes. The word "fish" is a hard 

 one to define because it is used in science with several different 

 grades of meaning. Ordinarily it is the name of a cold-blooded 

 vertebrate which is adapted for life in the water, and has its limbs, 

 if present, developed as fins, never as fingers or toes. This is the 

 broadest correct definition. It excludes the whales, porpoises and 

 seals, which are warm-blooded mammals, looking like fishes only 

 because they lead a fish-like life. It excludes the frogs and sal- 

 amanders of all grades because even those which have gills and 

 live in the water have fingers and toes instead of fins. But for 

 scientific purposes we usually adopt a narrower definition. We 

 exclude the tunicates, which have no skull and lose the backbone 

 in the course of development. We pass by the lancelets, fish-like 

 certainly, but having neither brain nor skull. The higher group of 

 lampreys is also excluded from the circle of fishes, for the lamprey 

 has no jaws, no limbs, and no trace of the bones to which limbs 

 should be hung. This would leave us, then, the following defin- 

 ition of a fish: A "fish" is a cold-blooded vertebrate adapted for 

 life in the water; breathing by means of gills which are attached to 

 bony or cartilaginous gill-arches; having the skull well-developed 



XXVI 



