SILURID.E THE CATFISHES 175 



the waters they enter and inhabit. By their services as scaven- 

 gers, they help to protect more sensitive fishes from the effects 

 of the pollution of the water through a decomposition of objects 

 which they are themselves very willing to devour, and in this 

 way also they may convert into a form acceptable to other 

 fishes food substances otherwise useless. As we have found 

 them to be eaten more or less by both our species of black bass, 

 by the sand-pike (Stizostedion canadense], and by the yellow 

 bullhead and the mud-cat, their utility in this sense seems 

 appreciable. 



On the other hand, it must be noticed that they have ap- 

 peared very rarely in the food of fishes, in comparison with their 

 numbers and general distribution. Only nine fishes out of more 

 than 1,200 examined had eaten them, while 45 of these same 

 fishes had eaten more or less freely of a single species of another 

 family the gizzard-shad. Reviewing the food of the catfishes 

 themselves, it seems to us clear, from our present data, that they 

 devour other fishes much more generally than others devour 

 them that whatever tends to their multiplication and contin- 

 uance tends rather to diminish the number of other species in 

 our waters than to increase them. Their partial immunity is 

 doubtless due in considerable measure to their remarkable 

 defensive apparatus of stiff, acute, projecting, poisoned spines 

 in the pectoral and dorsal fins, weapons capable of inflicting 

 really painful punctures in animals as large as man. These 

 fin-spines are evidently an advantageous substitute for the 

 defensive armor of scales which our catfishes have lost in the 

 course of their evolution. 



The nocturnal habits of catfishes must also contribute to 

 their protection from predaceous enemies, and the wide range 

 of their dietary enables them to exist in much larger numbers 

 than would be possible if their choice of food were more restricted. 

 Where one kind fails them for a time they may find an abundance 

 of another. Their power to crush the shells of many mollusks 

 and to reject the fragments gives them access to a means of 

 subsistence very abundant in many of the waters which they 

 inhabit, and available to but few other fishes, and their habit 

 of leading and guarding their young of course greatly increases 

 their chances of survival. 



Our catfishes are not by any means all of equal habit, or of 

 similar distribution and geological relationship. The stonecats 

 remain the size of minnows and the channel-cats are among the 



