258 Evolution and Adaptation 
the lower side in the metamorphosis is an hereditary charac- 
ter, and not a change produced in each individual by the 
withdrawal of the lower side from the action of light. On 
the other hand, the experiments show that the absence of 
pigment-cells from the lower side throughout life is due to 
the fact that light does not act upon that side, for, when it is 
allowed to act, pigment-cells appear. It seems to me that 
the only reasonable conclusion from these facts is, that the 
disappearance of pigment-cells was originally due to the 
absence of light, and that the change has now become 
hereditary. The pigment-cells produced by the action of 
light on the lower side are in all respects similar to those 
normally present on the upper side of the fish. If the dis- 
appearance of the pigment-cells were due entirely to a 
variation of the germ-plasm, no external influence could 
cause them to reappear, and, on the other hand, if there 
were no hereditary tendency, the coloration of the lower 
side of the flatfsh when exposed would be rapid and 
complete.” ! 
This evidence might be convincing were it not weakened 
by two or three assumptions. In the first place, it is not 
shown that if the loss of color on the lower side had been 
the result of the inheritance of an acquired character that 
the results seen in Cunningham’s experiment would follow 
as a consequence. Thus one of the starting-points of the 
argument really begs the whole question. In the second 
place, it is unproven that, had the loss of color of the lower 
side been the result of a variation of the germ-plasm, no ex- 
ternal influence could cause it to reappear. In this connec- 
tion there is another fact that has a bearing on the point here 
raised. In some species of flatfish the right side is turned 
down, and in other species the left. Occasionally an indi- 
vidual is found in a right-sided species that is left-sided, and 
in such cases the color is also reversed. Now, to explain this 
1 Natural Science, October, 1893. 
