FISHES: PISCES. 



h. 



N the Fishes, the last class of vertebrated animals, the chief and most obvious 

 C? jM distinction lies in their adaptation to a sub-aqueous existence, and their unfitness 

 ^^UlU for life upon dry land. 



There are many vertebrate animals which pass the whole of their lives in the 

 water, and would die if transferred to the land, such as the whales and the whole 

 of the cetacean tribe, an account of which may be found in Vol. I., page 418. But 

 these creatures are generally incapable of passing their life beneath the waters, as 

 their lungs are formed like those of the mammalia, and they are forced to breathe atmospheric 

 air at the surface of the waves. And though they would die if left upon land, their death 

 would occur from hunger and inability to move about in search of food, and in almost every 

 case a submersion of two continuous hours would drown the longest breathed whale that swims 

 the seas. 



The Fishes, on the contrary, are expressly formed for aquatic existence ; and the beautiful 

 respiratory organs, which we know by the popular term of "gills," are so constructed that 

 they can supply sufficient oxygen for the aeration of the blood. They have not the power, as 

 is sometimes imagined, of separating the oxygen, which, in its combination with certain pro- 

 portions of hydrogen, compose the element in which they live, but are able to take advantage 

 of the atmospheric air which is contained in the water. 



Any reader who happens to possess a globe with gold-Fish can prove, and doubtlessly has 

 proved, the truth of this assertion. It often happens that when the supply of water is insuffi- 

 cient, or the mouth of the vessel too small to permit the air to be absorbed by the water in 

 sufficient volume, the Fish come gasping to the surface, and there swim with gaping mouths, 

 sucking in the air with audible gulps. But if a little water be taken up in a cup or spoon, aud 

 dashed back from a little height, so as to cause a sharp splash, or, better still, if a syringe be 

 employed for the same purpose, so as to drive a quantity of atmospheric air into the water, the 

 Fish soon become contented, their anxious restlessness abates, and they quietly swim back- 

 ward and forward, without displaying any more signs of uneasiness. 



The reason that Fishes die when removed from the water, is not because the air is poison- 

 ous to them, as some seem to fancy, but because the delicate gill membranes become dry and 

 collapse against each other, so that the circulation of the blood is stopped, and the oxygen of 

 the atmosphere can no longer act upon it. It necessarily follows, that those Fish whose gills 

 can longest retain moisture will live longest on dry land, and that those whose gills dry most 

 rapidly will die the soonest. The herring, for example, where the delicate membranes are not 

 sufficiently guarded from the effects of heat and evaporation, dies almost immediately it is 

 taken out of the water; whereas the carp, a fish whose gill-covers can retain much moisture, 

 will survive for an astonishingly hum' time upon dry land, and the anabas, or climbing perch, 

 is actually able to travel from one pool to another, ascending the banks, and even traversing 

 hot and dusty roads. 



The entire shape of these creatines, subjected though it be to manifold variations, is 

 always subservient to the great object of passing rapidly through the ponderous liquid in 

 which they swim, so as to enable them to secure their prey or avoid their enemies. Even in 

 creatures of such different shapes as the sharks, the eels, the salmon tribe, and the flat fish, the 



