372 ZOOLOGY 



they form and accumulate electrical energy which may be dis- 

 charged at the will of the animal. This power certainly has a 

 protective value, as the discharge is in some cases powerful 

 enough to paralyze much larger animals than the fish itself. It 

 is probably useful also in capturing prey. 



Fig. i86. 



Fig. 186. Young Sea-bass {Cenlropristis siriatus). Photo from life by Dr. R. W. Shufeldt. 



Question on the figure. — Locate the pelvic fin and compare with other fish as to 

 position. 



Asymmetry. — In the flat-fishes we find a very striking com- 

 pression from side to side. In early life they have the position 

 normal to other fish, but in the adult stage they rest and swim 

 with the dorso-ventral plane horizontal instead of vertical — on 

 the left side in some species and on the right in others. The side 

 that is uppermost becomes pigmented like the back, and the 

 under side loses its pigment and becomes white, as the belly of 

 fishes in the normal position. The eye which belongs to the 

 under side changes its position until it comes to lie on the upper 

 side. The bones of the cranium, especially those about the eye, 

 are twisted and the right and left branches of the jaw are un- 

 equally developed. The dorsal and ventral fins become con- 

 tinuous and the body tends to become bilaterally symmetrical 

 in the new position. We can scarcely doubt that this asym- 

 metrical condition has been brought about by the position 

 which the animal takes in relation to the environment, but we 

 know that in some species the eye begins to migrate now before 

 the fish assumes the lateral position. 



