82 OUTLINES OF NATURAL HISTORY. 



Tlie Perch is one of the commonest of British and 

 European fishes, exclusively inhabiting fresh water. " It 

 is a gregarious fish, and loves deep holes and gentle 

 streams." It is also exceedingly voracious, and it will 

 live for some hours out of water. It attains a weight of 

 eight or nine pounds ; but this is quite exceptional, and a 

 Perch of three pounds weight is unusually large. Its 

 colours, when aUve, are very brilliant — green above, 

 passing into yellow below, with dark transverse bands on 

 the sides, and with the unpaired fins bright red. 



Recapitulation of Essential Characters. — The 

 animal is a water-breather, and the breathing-organs are 

 in the form of giUs. The limbs, when present, are con- 

 verted into " fins." The heart is (with few exceptions) 

 only two-chambered, and the blood is cold. Nearly 

 universal, though not quite, are the possession of a covering 

 of scales, the existence of a swim-bladder, and the fact that 

 the nose does not open behind into the throat. By these 

 characters the class Pisces is distinguished as a whole. 



CHAPTEPt XX. 



class amphibia. 



The Ampliihia are a class of animals which may be re- 

 garded as in many respects intermediate between the true 

 Reptiles and the Fishes, and they derive their name from 

 the fact that they mostly inhabit the water when young, 

 and live upon the land when old, or from the fact that 

 they live indifi"erently either on the land or in water 

 (Greek, amplii, both ; hios, life). As an example of 

 this class we may take the common Frog of Britain [Rana 

 temporaria). 



The peculiarities of the Frog will be most clearly under- 

 stood if we commence with the animal from the egg and 



