FISHES. 221 
rapidity. Some are occasionally met with in which the 
sides are alike in color, most often dark, but sometimes 
white, and these are said to be “doubles.” The fishes 
of this family differ from all other Vertebrates in a lack 
of perfect symmetry in relation to the two halves of the 
body. In all other Vertebrates the two halves are alike, 
except in some of the internal organs. But in these 
fishes there is a difference between the two sides in sev- 
eral particulars. The two eyes are on one side, and are 
irregularly placed ; in some species they are on the right 
side, and in others on the left. With this there is an 
irregularity in the bones of the head, while in all other 
Vertebrates they are alike on the two sides. Then there 
is the difference in color. There is also a difference in 
the pectoral fins, one being longer than the other. 
374. Most of the species of this family belong exclu- 
sively to the sea, and yet the Flounder and some others 
occasionally ascend rivers. The Halibut, so well-known 
in this country, is a very large fish, sometimes six or 
seven feet long, and weighing four or five hundred 
pounds. The flesh of the Turbot is considered peculiar- 
ly fine, and immense quantities are taken in the fisher- 
ies. Carpenter states that the Dutch receive £80,000 per 
annum for the supply of this fish to the London market. 
375. The Herring family furnish a great amount of 
food to man. They are mostly marine fishes; only a few 
species, among which is the Shad, ascending the rivers 
at the spawning season. The common Shad of this coun- 
try has a much better flavor than the Shad of Europe. 
The Sardine and Anchovy are aberrant species of this 
family. The true Herring inhabits the northern seas, 
and arrives every year in vast legions on the coasts of 
America, Europe, and Asia, never descending below the 
45th degree of north latitude. They come to the coast 
to spawn, and then retire to the depths of the sea, going 
northward. 
(376. The Eels are called Apoda, or Footless Fish, be- 
