130 LOWER VERTEBRATES. 



sluggish streams. In domestication numerous varieties of the carp have been formed, 

 the " leather-carp " (Lederkarpfen) being scaleless, others, " mirror-carp " (Spiegelkarp- 

 fen), having rows of large scales only along the lateral line, or the bases of the fins. 



Closely allied to the carp is the gold-fish (Carassius auratus). This is also a 

 common Chinese fish, introduced in domestication into Europe and America,. The 

 golden yellow color is found only in domesticated specimens, and is retained by 



I'lG. 8B. — a, Ojprinus carpio, carp; b, mirror-carp; o, Carassius auratus, goldflsh; d, JBarbus barhus, barbel. 



artificial selection. The native goldfish is olivaceous in color, and where the species 

 has become naturalized (as in the Potomac River, where it has escaped from fountains 

 in Washington) it reverts to its natural greenish hue. The gold-fish is valued solely for 

 its bright colors as an ornamental fish. It has no beauty of form, nor any interesting 

 habits, and many of our native fishes (Percidas, Cyprinidee) far excel it in attractive- 

 ness as aquarium fishes. Unfortunately they are less hardy. Many varieties and 

 monstrosities of the gold-fish have been produced by domestication. 



Allied to the carp is the barbel (JBarbus barbus), which abounds in the rivers of 



