10 NATURAL HISTORY. 



smother, because it has no air ; and this is also the case 

 in water from which the air has been driven by boiling. 

 These are satisfactory proofs that breathing by gills is 

 possible only in Avater containing air. The next question 

 may then be, Why do fish so readily die on being taken 

 out of the water ? there is still air to breathe, and it 

 may be more easily taken into the gills than that con- 

 tained in water. The answer is as follows. As soon as 

 a fish is taken out of the water, the coverings of the fine 

 laminas of the gills begin to lose their elasticity, and, ad- 

 hering to one another, prevent the free circulation of the 

 blood through their minute vessels ; and this increasing 

 the longer these organs are exposed to the influence of the 

 atmosphere, they ere long become dry, and the fish dies. 

 Some of the species, perhaps not so tender, or of which 

 the bronchiae, by some different arrangement of their 

 external organs, are not so susceptible of becoming dry 

 quickly, can, by being surrounded with damp substances, 

 sustain life for a considerable length of time. Carp, 

 enveloped in moss and kept wet, are conveyed great dis- 

 tances, and can be preserved alive for many days in cel- 

 lars ; and eels, too, in damp nights, often leave the water 

 to seek for food on land. 



The whole structure of fishes is as perfectly arranged 

 to serve them for swimming as that of birds is adapted for 

 flying. Living in an element of nearly the same specific 

 gravity as their own bodies, they do not require extended 

 members to support them or aid their movements. The 

 forward motion is effected by the expanded horizontal fins. 

 The tail, serving as a rudder, enables the fish to direct its 

 course, whether upward, downward, right or left. These 

 fins, which represent forefeet, are called the pectoral fins; 

 those placed farther backwards are called the abdominal 



