Animals Before Man 



this they had trimmed the tail part of the mem- 

 brane too close, so that the upper and lower 

 fins (dorsal and caudal) were obliged to play 

 the part of a tail. Such a thing really hap- 

 pens in at least 

 one modern fish, 

 the extraordinary 

 salt-water sunfish 

 or mola, in which 

 the tail has com- 

 pletely vanished, 

 its place, so far 

 as swimming is 

 concerned, being 

 taken by the fins. 

 None of the early 

 fishes had tails of 

 the symmetrical 

 shape and com- 

 plex structure we 

 see among the bony or true fishes of to-day, and 

 in these ancient forms it is easily seen that the 

 tail probably once formed part of a continuous 

 fin. Some of them, however, mimicked the 



102 



The ocean sunfish, Mola mola, a fish 

 which has lost its tail. 



