6 The Life of the Fish 
in it of salts of lime. One of these is called the opercle, or 
gill-cover, and before it, forming a right angle, is the pre- 
opercle, or false gill-cover. On our sunfish we see that the 
opercle ends behind in a long and narrow flap, which looks 
like an ear. This is black in color, with an edging of scarlet 
as though a drop of blood had spread along its margin. 
When the fish is in the water its back is dark greenish-looking, 
like the weeds and the sticks in the bottom, so that we cannot 
see it very plainly. This is the way the fish looks to the fish- 
hawks or herons in the air above it who may come to the stream 
to look for fish. Those fishes which from above look most like 
the bottom can most readily hide and save themselves. The 
under side of the sunfish is paler, and most fishes have the belly 
white. Fishes with white bellies swim high in the water, and the 
fishes who would catch them lie below. To the fish in the water 
Fie. 3.—Common Sunfish, Lupomotis gibbosus (Linneus). Natural size. (From 
life by R. W. Shufeldt.) 
all outside the water looks white, and so the white-bellied fishes 
are hard for other fishes to see, just as it is hard for us to see a 
white rabbit bounding over the snow. 
