36 ANATOMY AND PHYSIOLOGY 



rope has its appropriate place ; but, owing to the 

 little obliquity of their direction, the muscles act 

 to very great disadvantage. If the bones were 

 provided with long projecting processes, as in the 

 bones of land animals, they would have retarded 

 the motion of the fish through the water ; it was 

 necessary, therefore, in the economy of their na- 

 tures, to sacrifice the mechanical advantage of nu- 

 merous levers, that facility might be afforded to 

 their easy movement in their destined element. 

 Those muscles which control the fins and jaws, 

 are short, well developed and strong in contraction: 

 those on the sides, take a winding direction, and 

 consequently cannot act in producing short curves. 

 The object to be attained, in this conformation, 

 was ample security of the viscera, with a sub- 

 stance that would give power to exert power. 



CIRCULATION OF THE BLOOD. 



A single heart, an organ containing only two 

 cavities, instead of four, as in mammalia ; circu- 

 lating cold blood, which in terrestrial animals is 

 warm, gives additional interest to the natural his- 

 tory of the beings under consideration ; in them, 

 the heart does not propel the vital fluid through 

 the system, — which presents another extraordi- 

 nary circumstance in their organization. The 



