INTRODUCTION. 65 



lungs. It is of various shapes, sometimes seeming 

 like a simple bag extending the whole length of 

 the cavity, sometimes cut as it were in two, by 

 a narrow stricture, and having the appearance of 

 two irregular sacks. The supply of air can be 

 compressed by muscular action, and accordingly 

 will serve to assist in raising or sinking the 

 animal ; and it is remarkable, that in those fishes 

 which reside much at the bottom, and seldom 

 or never come to the surface, this organ is almost 

 always wanting. 



But independent of the common manner of 

 progressive motion among fishes, other means 

 have been given them, by which either a great 

 accession of power is added; or where the ordinary 

 limbs are small, or wanting, organs of an entirely 

 different nature have been constructed. In a genus 

 of fishes, mentioned by almost all travellers as 

 amusing the weariness of a long sea voyage, the 

 immense development of the pectoral fins, and 

 the power the animal possesses of raising and sus- 

 taining itself for a considerable time above the 

 waves, has gained for it the epithet of Flying. 

 The action, however, appears to have more re- 

 semblance to a long and vigorous leap, than to 

 flight as practised by the denizens of the air. A 

 difference of opinion exists as to the motion of 

 the pectoral fins, whereby they are for the time 



E 



