TYPES OF FINS. 



147 



distinctly seen. Now we 

 liave already mentioned that 

 modern sharks and rays have 

 fan-like fins ; and it is, 

 therefore, clear that both in 

 the sharks and in the com- 

 pound group represented by 

 the ganoid and the bony 

 fishes there has been an in- 

 dependent transition from the 

 fringe-finned to the fan-finned 

 type. On the other hand, 

 in the lung-fishes, which, 

 as we shall see shortly, are a 

 very ancient race, the fringe- 

 finned structure has been 

 preserved without alteration 

 throughout countless ages. 



We are still unacquainted 

 with the habits of some of the 

 living fringe-finned fishes, but 

 at least the lung-fishes are 

 species living partially buried 

 in the mud, and are evidently 

 not adapted for swimming 

 rapidly. On the other hand, 

 the fan-finned modem fishes^ 

 whether they be sharks or 

 whether they be bony fishes, 

 are generally adapted for 

 rapid motion in the water. 

 Any person who has watched 

 a bowl of gold-fish will not 

 have failed to notice the 

 incessant and rapid motion 

 of their film-like fins, and it 

 IS quite evident that this 

 rapid motion could only be 

 produced by fins of the fan- 

 like structure. The fringe-fins 

 L 2 



