HEREDITY. 429 



that for three-fourths of a century, that it has gone on 

 along with systematic exercise of special function in 

 successive generations of the present fast trotters, is 

 indisputable and very evident. Selection has doubt- 

 less determined the proper correlation of the various 

 organs involved in the special evolution, but the in- 

 crease in speed has only come along with the func- 

 tional development, which was enhanced by special 

 exercise in the individuals of successive generations. 

 The cumulative value of this, if transmitted, would be 

 vastly more than enough to account for all the increase 

 that has actually occurred, great as that is. Viewed 

 as phenomena, there is every appearance and indica- 

 tion that the changes acquired by individuals through 

 the exercise of function have been to some degree 

 transmitted, and have been cumulative, and that this 

 has been one factor in the evolution of speed. The 

 cumulative variation has been most marked since we 

 have had a 2:30 class, that is, since we have produced 

 animals that are swift by heredity, and whose ances- 

 tors, as well as themselves, have been exercised and 

 trained to trot. Studied as phenomena, there is not a 

 particle of evidence that these special changes ac- 

 quired by the individuals were totally lost to each suc- 

 cessive generation, and that all that was ' transmitted 

 by heredity,' was a something that did not exist in 

 either parent or in any ancestor. There is nothing 

 whatever in the actual phenomena observed anywhere 

 along the line of this development of speed that would 

 lead us to even suspect that the changes due to exer- 

 cise of function had not been a factor in the evolution, 

 and there is not a particle of evidence, other than met- 

 aphysical deductions, much less proof, that it would 



