AFFINITIES OF THE ELASMOBRANCHS 



95 



anterior element of the fin stem, by being raised or de- 

 pressed, comes to direct the upward or downward motion 

 of the fish. In this mode of movement seems to have 

 been paralleled the undulation of the ancestral fin fold. 

 On the fish's dorsal side colour adaptations have become 

 marked, the ventral 

 aspect becoming de- 

 ficient or wanting in 

 pigment. In its hab- 

 its the skate mimics 

 the colour of the 

 bottom and glides 

 along inconspicuous- 

 ly, apparently with- 

 out movement ; when 

 alarmed, it will press 

 its enlarged and flat- 

 tened fins so closely 

 to the bottom that it 

 appears to adhere, 

 and is to be dislodged 

 only with the great- 

 est efforts. 



Two of the aber- 

 rant forms of rays are 

 shown in Figs. 102 

 and 102 A. The for- 

 mer, the Torpedo, is remarkable on account of its electric 

 organs ; the latter, Dicerobatis, on account of the great 

 breadth of its pectorals, and its enormous size. 



Fig. 102. — The torpedo, Torpedo occidcnta- 

 lis, Storer. J'. X |. (After GOODE in U. S. 

 F. C.) 



