The Food of Fishes. 27 



little fishes, and opens up the question of their origin as a 

 group. 



The close relation of the Etheostomatidae to the Percidae 

 requires us to believe that the two groups have but recent- 

 ly diverged, if, indeed, they are yet distinctly separate. 



We must inquire, therefore, into the causes which have 

 operated upon a group of percoids to limit their range to 

 such apparently unfavorable situations, to diminish their 

 size, to develop unduly the paired fins and reduce the 

 air-bladder, to remove the scales of several species more 

 or less completely from the head, breast, neck, and ventral 

 region, and to restrict their food chiefly to the few forms 

 mentioned above. 



No species can long maintain itself anywhere which can 

 not, in some way, find a sufiicient supply of food, and also 

 protect itself against its enemies. In the contest with its 

 enemies it may acquire defensive structures or powers of 

 escape sufficient for its protection, or a reproductive ca- 

 pacity which will compensate for large losses, or it may 

 become adapted to some place of refuge where other fishes 

 will not follow. What better refuge could a harassed fish 

 desire than the hiding-places among stones in the shallows 

 of a stream, where the water dashes ceaslessly by with a 

 swiftness few fish can stem? And if, at the same time, 

 the refugee develops a swimming power which enables it 

 to dart like a flash against the strongest current, its safety 

 would seem to be insured. But what food could it flnd in 

 such a place? Let us turn over the stones in such a stream, 

 sweeping the roiled water at the same time with a small 

 cloth net, and we shall find larvae of Chironomus and 

 small ephemerids and other such prey, and little else — 

 food too minute and difficult of access to support a large 

 fish, but answering very well if our immigrant can keep 

 down his size. Here the principles of of natural selection 

 assert their power. The limited supply of food early ar- 

 rests the growth of the young ; while every fish which pas- 

 ses the allowable maximum is forced for food to brave the 

 dangers of the deeper waters, where the chances are that 

 it falls a prey. On the other hand, the smaller the size of 

 those which escape this alternative, the less likely will 



