NATURAL HISTORY. 413 



water from flowing in the proper direction, so that it is per- 

 fectly possible to drown a fish ; although L'Estrange may doubt 

 the fact : 



"And like those sages that would drown a fish, 

 1 am condemn'd to suffer what I wish." 



Most anglers are perfectly aware of the power obtained by keep- 

 ing the head of a hooked fish doivn the stream. 



The elongated form of fishes, and their smooth covering, af- 

 fording but little resistance to the water, beautifully show their 

 perfect adaptation for the element in which they reside. 



Their rapid movements through the water are principally 

 performed by means of a lateral vibration of the tail, just as a 

 boat is sculled along by a single oar at the stern, or by a con- 

 stant vibration of the rudder.^ The fins serve principally as 

 balancers. 



Most fish possess a singular organ called the " swimming- 

 bladder." This is a membranous pouch, varying exceedingly 

 in size and shape, situated close under the spine, and filled by 

 some means with gas, mostly found to be nitrogen, but in deep- 

 sea-fishes, an excess of oxygen is discovered to exist. The fish 

 seems to be able to rise or sink by means of compressing or 

 expanding this pouch, without being forced to make use of its 

 tail or fins. 



The smooth scaly covering with which most fish are fur- 

 nished, is admirably fitted both for defence against the water, 

 and for enabling the fish to glide easily through places where 

 a rough covering would have held it prisoner. Many valuable 

 characteristics are derived from the shape of the scales in dif- 

 ferent fish. There are four principal varieties, called, 1. Pla- 

 coid, or flat scales; 2. Ganoid, or polished scales; 3. Ctenoid, 

 or toothed scales ; and 4. Cycloid, or circular scales. f 



The Acanthopterygii are so called from their spinous fin rays. 

 Those of the Perch are excellent examples. 



The RED GURNARD, or CUCKOO GURNARD, as it is. sometimes 

 called from the sound it utters when taken out of the water, 

 is very common on the English coast. It is rather a small 



* The dead and mangled carcase of a flensed whale has been frequently known to 

 swim for a considerable distance by the mere force of the muscular movements of the 

 tail after death. 



t These names are derived from, 1 . TrAuKoff, flat ; 2. yav6u, I polish ; 3. KTCIS , KTF. v6f, 

 acornb ; 4. KikAoi, a circle. The scales of the 1. Dogfish ; 2. Sturgeon ; 3. Perch ; and 

 4. Carp, are excellent instances of the four kinds of scales. 



