1889.] 541 fRyder 



Iroofs of the Effects of Habitual Use in the Modification of Animal 



Organisms. 



By Prof. John A. Ryder. 



{Read before the American Philosophical Society, October IS, 18S9.) 



Much has been written in regard to the supposed effects of use in induc- 

 ing more or less permanent and inheritable alterations in the structure of 

 animal forms. Darwin lays stress upon the effects of disuse in weakening 

 the muscles which control the movements of the ears. He supposes, on 

 the ground of disuse, that the drooping ears of the many domesticated 

 races and species of mammals may have thus arisen. He also urges the 

 same argument to account for the poorly developed and almost abortive 

 eyes of moles and certain rodents. To decreased use he attributes the 

 origin of the lighter wing-bones of domesticated races of ducks, while 

 their relatively stronger leg-bones he attributes to increased use. He also 

 supposes that the increased dimensions of the udders of cows and goats 

 are partly to be attributed to the effects of unwonted and more prolonged 

 use when bred from generation to generation for purposes of milking. 

 He also cites approvingly the results of the experiments of Ranke, who 

 showed that the flow of blood is greatly increased towards any part which 

 is performing work, and again sinks or diminishes in amount when the 

 part is at rest, concluding that, if the work is frequently recurrent, the 

 vessels increase in size and the part is better nourished. From the fre- 

 quent reference to the effects of use and disuse and his evident belief that 

 such effects were inherited, it is clear that Mr. Darwin attached great im- 

 portance to use and disuse as an agent in modifying species. In so far as 

 Mr. Darwin appealed to the .effects of use and disuse he followed the lead 

 and accepted some of the conclusions of his great predecessor, Lamarck, 

 who had published his own views more than fifty years before the appear- 

 ance of the " Origin of Species." 



Lately much activity has been manifested by the German biologists, 

 under the leadership of Prof Weismann, in testing the effects of the 

 inheritance of mutilations in reference to the question of use and disuse. 

 It is the opinion of the present writer that the method of experimentation 

 resorted to by Weismann is altogether unsatisfactory, since the mutila- 

 tions in the first place were made upon parts which were not only already 

 rudimentary, but also after the ontogenetic processes had been practically 

 completed. Weismann practiced the excision of the tails of mice in a 

 series of successive generations without any inherited result, and forth- 

 with concludes that mutilations are not inherited. This negative evi- 

 dence, based on experiments in mutilating mice, is of absolutely no value 

 whatever in solving the problem of the effects of use and disuse now 

 before the present generation of biological investigators, as I hope to show 



