1880.] The Food of the Darters. 701 
large losses, or it may become adapted to some place of refuge 
where other fishes will not follow. What better refuge could 
a harrassed fish desire than the hiding places among stones 
in the shailows of a stream, where the water dashes ceaselessly 
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 ensured. But what food could it find in stich 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— 
larvee 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 natural selection assert 
their power. The limited supply of food early arrests the growth 
of the young; while every fish which passes the allowable maxi- 
mum 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 they be to attract the appetite of the small gar or 
other guerilla which may occasionally raid their retreat, and the 
more easily will they slip about under stones in search of their 
microscopic game. 
Like other fishes, the darters must have their periods of repose, 
all the more urgent because of the constant struggle with the 
Swift current which their habitat imposes. Shut out from the 
deep still pools and slow eddies where the larger species float 
Suspended in mid stream, they are forced to spend their leisure 
on or beneath the bottom of the stream, resting on their extended 
pectorals and anal, or wholly buried in the sand, Possibly this 
fact is correlated with the absence or rudimentary condition of 
the air-bladder; as it is a rule with many exceptions—but still, 
probably, a rule—that this organ is wanting in fishes which live 
chiefly at the bottom. 
Doubtless the search for food has much to do with this selec- 
tion of a habitat. I have found that the young of nearly all 
Species of our fresh-water fishes are competitors for food, feed- 
ing almost entirely on entomostraca and the larve of minute 
In Boleosoma, which is normally scaled in front of the dorsal fin, we often find 
the skin of this region bare in large specimens, and showing evident signs of 
rubhing, ; 
