Darwin's Artificial and Natural Selection 137 
that the evidence in favor of the inheritance of acquired 
characters is very doubtful at best, may we not conclude 
that Mivart’s criticisms have sometimes hit the mark? 
The following objection appears to be a veritable stum- 
bling-block to the theory. Flatfishes and soles lie on one 
side, and do not stand in a vertical position as do other fish. 
Some species lie on one side and some on the other, and 
some species contain both right-sided and left-sided indi- 
viduals. In connection with this unusual habit we find a 
striking change in the structure. The eye that would be on 
the under side has shifted, so that it has come to lie on the 
upper side of the head, z.e. both eyes lie on the same side, — 
a condition found in no other vertebrate. As a result of the 
shifting of the eye, the bones of the skull have also become 
profoundly modified. The young fish that emerge from the 
egg swim at first upright, as do ordinary fish, and only after 
they have led a free existence for some time do they turn 
to one side and sink to the bottom. Unless the under eye 
moved to the upper side it would be of no use to the flatfish, 
and might even be a source of injury. Mivart points out 
that a sudden, spontaneous transformation in the position of 
eye is hardly conceivable, and to this Darwin, of course, 
assents. Mivart adds: “If the transit was gradual, then 
how such transit of one eye a minute fraction of the journey 
towards the other side of the head could benefit the indi- 
vidual is, indeed, far from clear. It seems even that such an 
incipient transformation must rather have been injurious.” 
Darwin’s reply is characteristic : — 
“We thus see that the first stages of the transit of the 
eye from one side of the head to the other, which Mr. Mivart 
considers would be injurious, may be attributed to the habit, 
no doubt beneficial to the individual and to the species, of 
endeavoring to look upwards with both eyes, whilst resting 
on one side at the bottom. We may also attribute to the 
inherited effects of use the fact of the mouth in several kinds 
