THE FACTORS OF ORGANIC EVOLUTION. 



115 



ample, Professor Cope argues very ably that bones are 

 lengthened by both stretch and impact, and that modifi- 

 cations thus produced are inherited. Even granting 

 that this is true, how would it be possible for this pro- 

 cess of lengthening to cease, since in active animals the 

 stretch and impact must be continual ? Professor Cope 

 answers that the growth ceases when " equilibrium " is 

 reached. I confess I can not understand this explana- 

 tion, since the assumed stimulus to growth must be con- 

 tinual. But, granting again that growth may stop when 

 an animal's legs become long enough to " satisfy its 

 needs," how on this principle are we to account for the 

 shortening of legs, as, for example, in the turnspit dog 

 and the ancon sheep and numberless cases occurring in 

 Nature ? If any one species was able, by taking thought 

 of mechanical stresses and strains, to add one cubit unto 

 its stature, how could the same stresses and strains be 

 invoked to decrease its stature ? 



These evidences are, I know, not the strongest ones 

 which can be adduced in support of the Lamarckian 

 factors. There are at present a relatively small num- 

 ber of such arguments which seem to be valid and the 

 great force of which I fully admit. But the cases which 

 I have cited are, I believe, fair samples of the majority 

 of the evidences so far presented, and in the face of 

 such " evidence " it is not surprising that one who is 

 himself a profound student of the subject and a con- 

 vinced Lamarckian prays that the Lamarckian theory 

 may be delivered from its friends.* 



6. Another line of evidence, and by far the most 

 promising, is that of direct experiment. So far, most 

 of the experiments which have been carried on to deter- 

 mine this question have been carried only halfway to a 



* H. F. Osborn. Evolution and Heredity. Biological Lec- 

 tures, 1890. 



