Inheritance of Acquired Characters 259 
in the way suggested by Cunningham, we should be obliged 
to assume that some of the ancestors acquired the loss of 
pigment on one side of the body, and others on the other 
side according to which side was turned down. This suppo- 
sition might be appealed to to give us an explanation of the 
occasional reversal of the symmetry as a rare occurrence 
at the present time; but the argument is so transparently 
improbable that, I believe, the Lamarckian school would 
hesitate to make use of it, yet, in principle, it is about the 
same as that Cunningham has followed above. 
If, on the other hand, we suppose the difference in color of 
the two sides to have been the result of a germ-variation, we 
need only suppose that this was of such a kind that the color 
of the under side is only in a latent condition, and if an 
external factor can cause a reaction to take place on the light 
side, it is not surprising that this should call forth the latent 
color patterns. The result can be given at least a formal 
explanation on the theory that the original change was a 
germ-variation. 
We come now to the evidence derived from paleontology. 
A number of evolutionists, more especially of the American 
school, have tried to show that the evolution of a number of 
groups can best be accounted for on the theory of the 
inheritance of acquired characters. A point that we must 
always bear in mind is that evolution in a direct line need not 
necessarily be the outcome of Lamarckian factors. Some of 
our leading paleontologists, Cope, Hyatt, Scott, Osborn, have 
been strongly impressed by the paleontological evidence in 
favor of the view that evolution has often been in direct 
lines; and some, at least, of these investigators have been 
led to conclude that only the Lamarckian factor of the inheri- 
tance of acquired characters can give a sufficient explana- 
tion of the facts. Paleontologists have been much impressed 
by the fact that evolution has been along the lines which we 
might imagine that it would follow if the effects of use and 
