250 Evolution and Adaptation 



right direction occurred in the fore-quarters, it is unlikely that 

 similar variations would occur in the hind-quarters, etc. Yet 

 the feat has been accomplished, and while it is difficult to 

 prove that the inheritance of acquired characters has not had 

 a hand in the process, it is improbable that this has been the 

 case, but rather that artificial selection of some kind of vari- 

 ations has been the factor at work. 



So long as the Lamarckian theory is supported by argu- 

 ments like these, it can never hope to be established with any- 

 thing more than a certain degree of probability. If it is 

 correct, then its demonstration must come from experiment. 

 This brings us to a consideration of the experimental evidence 

 which has been supposed by some writers to give conclusive 

 proof of the validity of the theory. 



The best direct evidence in favor of the Lamarckian argu- 

 ment is that furnished by the experiments of Brown-Sequard. 

 He found, as the result of injury to the nervous system of 

 guinea-pigs, that epilepsy appeared in the adult animal, and 

 that young born from these epileptic parents became also epi- 

 leptic. Still more important was his discovery that, after an 

 operation on the nerves, as a result of which certain organs, 

 the ear or the leg, for instance, are affected, the same affec- 

 tion appears in the young born from such parents. These 

 results of Brown-Sequard have been vouched for by two of 

 his assistants, and his results in regard to the inheritance of 

 epilepsy have been confirmed by Obersteiner, and by Luciani 

 on dogs. Equally important is their later confirmation, as 

 far as the main facts go, by Romanes. 



Brown-Sequard gives the following summary of his results. 

 I follow Romanes' translation in his book on " Darwin and 

 after Darwin," where there is also given a careful analysis of 

 Brown-Sequard's results, as well as the outcome of the experi- 

 ments of Romanes himself. The summary is as follows : — 



1 . " Appearance of epilepsy in animals born of parents which 

 had been rendered epileptic by an injury to the spinal cord. 



