38 . CLASSIFICATION OF FISHES. 



how a fish can rest without any motion of its fins*, — 

 more especially those which habitually live in the open sea. 

 (39.) We have already shown in what manner the 

 fins of fishes represent the organs of motion in birds. 

 Now, in all these latter, superior powers of flight are 

 invariably indicated by the great length and pointed 

 structure of the wing ; and this power among birds is at 

 its maximum when the tail, also, is forked: the common 

 house swallow shows this in perfection. Now this is pre- 

 cisely analogous to what we see among fishes : all those 

 with pointed pectorals swim much faster than those which 

 have this fin rounded; an inference which does not merely 

 rest on analogical reasoning, but from the remarkable 

 fact, that the far greater majority of those fish which 

 have pointed pectorals habitually live in the open ocean, 

 or far from the shelter of the shore. We know not, 

 at this moment, of any freshwater genus, wherein the 

 pectorals fins are decidedly pointed ; while, if we look to 

 the oceanic families of the Zeidce and Scomberidce, and 

 even the majority of the Percidce and Chcetodonidce, we 

 shall find very few instances of the pectorals being 

 rounded. But if, in addition to this pointed form, a fish 

 has the tail also deeply forked, and the pectoral fins 

 falcated or curved, as are the wings of the goatsuckers 

 and humming birds, then we have the highest develop- 

 ment of the powers of swimming possessed by this class. 

 Hence it is that the mackerel, the sword-fish, and the 

 tunnies — more especially the latter — are, together with 

 the flying fish, the most perfect of all swimmers. Every 

 one who has seen the astonishing rapidity with which 

 the tunnies will sometimes play about a vessel in the 

 Atlantic Ocean, when sailing at its utmost speed, will be 

 perfectly convinced of this : for although their rapidity, 

 for a time, may not equal that of the rays, it is quite 

 evident that they have a vast superiority over the latter 

 in their adaptation for sustaining swimming ; the rays, 

 indeed, being obviously ground-fish, or of those fami- 

 lies which seek their prey at the bottom of the sea. The 



* Except the flat fish, which, of course, lie on the ground. 



