REPORT OF COMMISSIONERS OF INLAND FISHERIES. 53 



objections to these hypotheses. Cole and Johnstone," in an ex- 

 haustive paper on the anatomy and osteology of the Plaice {Pleu- 

 ronectes), have shown that the mechanical relations existing be- 

 tween the eye muscles and the bones of the frontal and prefrontal 

 region are such that the contraction of the eye-muscles could not 

 have caused the facial asymmetry. The suggestion that the weight 

 of the body of the fish when turned over on its side aided in pushing 

 the eye over onto the other side, apparently can not be invoked to 

 explains the appearance of asymmetery in the development of the 

 Individual, at least, since there seems to be no particular tendency 

 on the part of the larval fishes to turn over on its side until after the 

 eye has begun its migration. This is true of some species at any 

 rate, for Williamsf states that the specimens which he captured and 

 kept in the laboratory during the metamorphosis showed in resting 

 no preference for either side until the eye was near the mid-line. 

 If it. seems unlikely that larval fishes could have been modified in 

 this way, it seems even more improbable that the hypothetical 

 symmetrical ancestor in the adult form when the bones and other 

 structures had become fixed should have become modified in any 

 such way. Objections of a more general nature against the above 

 explanations are the objections which can be alleged against any 

 theory involving the assumption of the inheritance of acquired 

 characters, but such detailed criticisms of this theory of course have 

 no place in this paper. 



The question of the origin of the modifications of the flat-fishes 

 inevitably involves the general theories of evolution. Here it will 

 be possible, to consider only very briefly, the bearing of these theories 

 upon this problem. The development of the fiat-fish, as briefly 

 outlined above, shows that the asymmetery does not express itself 

 outwardly until some days after the fish is out of the egg, yet there 

 is evidence which seems to substantially sanction the inference that 

 for its origin in ontogeny, the asymmetry goes back to the germ. 

 That there is some real difference between the organization of the 



* Op. cit. 



tReference to the work cited will be found in the foot-note to page 79. 



