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 1 02 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. 



pig. 102. The torpedo, Torpedo occidcnta- 



* x * (After GOODE in u. S. 



