10 
cranium zn the region of the orbit 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 hes between 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 produced, 
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 
