14 BRITISH FRESH-WATER FISHES 
The mention of the Flat-fishes brings under notice the 
solitary and remarkable exception to the power of fish to 
i balance themselves in the water, forming as it does 
n exception : =) b> 
inthe the exclusive characteristic of the whole of one of 
Flatfishes: +6 two divisions of the Anacanthini, or Spineless 
Fishes, an order containing such important food fishes as the 
cod, ling, halibut, turbot, sole, etc. The Pleuronectide, or 
Side-swimmers, commonly termed Flat-fishes, undergo a series 
of metamorphoses unique, so far as is known, in animated 
nature, and certainly among vertebrate animals. For some 
time after leaving the egg they remain perfectly symmetrical, 
swimming, like other fishes, back uppermost, and carrying an 
eye on each side of the head. But as they grow older they 
lose their balance, turn over on one side, and, being un- 
provided with an air-bladder, sink to the bottom, which they 
can only leave henceforward by active swimming. The side 
next the ground becomes pearly white, like the bellies of most 
vertical swimmers, the upper or exposed side assuming tints 
closely assimilating in colour with the surrounding sand, rocks, 
mud, or weeds. Lastly, the eye on the side which falls under- 
most pushes itself either round or through the head, so as to 
take up a new and useful position on the “ business ” side of 
the face. Owing to the mouth retaining the position it received 
at first, this contortion of the eyes imparts a most grotesque 
expression to the countenance. 
It is no matter of accident which side happens to fall 
undermost. In the flounder, the only species which can be 
said to be a regular sojourner in English rivers, the fish 
reclines normally on its left side, though there are occasional 
exceptions to this rule. The turbot, brill, and some others 
recline on their right side ; but there occur also abnormal 
specimens of right-handed flounders and left-handed brill. 
On the whole, having regard to the enormous inroads 
made upon the numbers of the various kinds of flat-fishes by 
trawls and other’ expedients, and to the numbers in which the 
