214 THE THEORIES OF EVOLUTION 



by Voisin and Peron, 3 who explain that in epilepsy a 

 toxin is produced which affects the sexual cells. 



In other words no definite conclusion can be drawn 

 from these experiments as to the transmissibility of 

 acquired characters. Certain modifications, incontest- 

 ably due to some exterior influence, are observed to 

 reappear in the offspring. Plants, for instance, can 

 adapt themselves to a different climate. Those plants 

 sometimes present modifications which their ancestors 

 acquired progressively in the course of many genera- 

 tions ; cherry trees acclimatised in Ceylon acquire per- 

 ennial foliage (case cited by Detmar). But in all 

 similar cases, the causal factor is still exerting its 

 influence, and it is impossible to determine the part 

 played by heredity in making new characters constant. 



There are other cases, however, in which modified 

 plants taken back to the regions where they originated 

 retained for several generations the character acquired 

 under the influence of the previous change of climate. 



In the animal world there is the case of hereditary 

 transmission observed among Daphnae and which we 

 mention elsewhere. Here is another case: in the 

 course of experiments to determine the influence of 

 salt in various quantities on certain aquatic animals, 

 Ferroniere 4 transferred a Tubifeoc from fresh water 



s Archives de Neurologie, 1892-93, and Voisin: L'Epilepsie (Paris, 

 1897, p. 125-133), quoted by J. A. Thomson: Heredity, p. 235. 



4 Etudes biologiques stir la forme supralittorale de la Loire-Infe"rieure, 

 1901. 



