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 



