14 The Life of the Fish 
out nerves of motion and receives nerves of sense. Everything 
that is done by the fish, inside or outside, receives the attention 
of the little branches of the great nerve-cord. 
The Fish’s Nest.—The sunfish in the spawning time will 
build some sort of a nest of stones on the bottom of the eddy, 
and then, when the eggs are laid, the male with flashing eye and 
fins all spread will defend the place with a good deal of spirit. 
All this we call instinct. He fights as well the first time as 
the last. The pressure of the eggs suggests nest-building to 
the female. The presence of the eggs tells the male to defend 
them. But the facts of the nest-building and nest protection are 
not very well understood, and any boy who can watch them and 
describe them truly will be able to add something to science. 
