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 Hadrcpteriis, like those of Percma, 

 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. Hadroptcnis 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 MuUins, once said to us of 

 Thoreau. 



