10 



cranium in the region of the orhit has rotated on its longi- 

 tudinal axis to the right side, until the two eyes, instead 

 of occupying a horizontal plane, have assumed a vertical 

 one, and the left eye is dorsal to the right. Then the 

 dorsal fin grew forwards over the roof of the cranium, but 

 naturally cannot define the morphological right and left 

 sides of the orbital region. Thus the ocular side com- 

 -prises not only the right side but a portion of the left, 

 and the true morphological median line lies hetween the 

 two eyes and not above them. The relation of the eyes to 

 the skull is, notwithstanding the rotation of the orbital 

 region of the latter, exactly the same as in a symmetrical 

 fish, and the only differences of importance are the atrophy 

 of the anterior portion of the left frontal, and the purely 

 secondary junction under the left eye of the left prefrontal 

 and frontal (fig. 1). 



Now whilst the above is a satisfactory answer to the 

 question how, it does not help us with the question why. 

 It is to be presumed that the first stimulus to asymmetry 

 was an increasing tendency of the fish to lie on the sea 

 bottom on one side of its body. Cunningham then in- 

 vokes the principle of the inheritance of acquired charac- 

 ters, and believes that the torsion itself was produced by 

 the action of the eye muscles. We have considered this 

 point of view very carefully both 'per se, as a theory, and 

 also as a supposed explanation of the facts, with the result 

 that we cannot subscribe to Cunningham's conclusions. 

 It is to us simply inconceivable how any action of the eye 

 muscles, as they are found in fishes, could have pro- 

 duced the existing torsion of the head, and this quite 

 apart from the question whether such results, if jiroduced, 

 would have been inherited. This, however, will be 

 further referred to in the section on the eye. In the 

 meantime we prefer to believe that the asymmetry of the 



