JOHNNY DARTERS. 25 
the fishes seem to fade out; these blotches grow 
pale, and no longer meet; but in an instant they 
may regain their original form and shade. This 
latter change can be induced by the offer of food, 
and it is of course due to muscular action on the 
scales which cover the darker pigment. A male 
in our aquarium underwent almost instantly an en- 
tire change of coloration upon the introduction of a 
female fish of the same species recognized by him 
as his affinity. Although the two have been to- 
gether for some weeks, the novelty has not. yet 
worn off; and although his colors vary much from 
one hour to another, he has never yet quite re- 
verted to his original hues. The form of the black- 
sided darter is more graceful than that of any 
other, and his movements have little of that angu- 
lar jerkiness which characterizes his relatives. 
The fins of Hadropterus, like those of Percina, 
are long and large, the number of dorsal spines 
being about fourteen. A notable peculiarity in 
both species is the presence of a row of shields, or 
enlarged scales, along the middle line of the abdo- 
men. These may help to protect that part from 
the friction of the stony bottom. They seem to 
be shed sometimes; but when or why this happens 
we do not know. SHadropterus delights in clear 
running water, and may be found in most streams 
south and west of New York. It is especially de- 
sirable for aquaria, being hardier than any other 
fish as pretty, and prettier than any other fish as 
hardy, and withal with “a way of his own,” as an 
Irish laborer, Barney Mullins, once said to us of 
Thoreau. 
