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 Tays are Fig. 102.— The torpedo, Torpedv occidenta- 
z. loeen in Figs. 102 o% "ae dg. X44. (After GOODE in U. S. 
and 102 A. The for- — 
P ; _ mer, the Zorpedo, is remarkable on account of its electric 
. organs; the latter, Dicerobatis, on account of the great 
i breadth of its pectorals, and its enormous size. 
