OTHER WRITEES ON 'FLUCTUATIONS' 271 



number of generations, and that then the only further effect 

 of selection is to keep up the standard already arrived at ' 

 (pp. 135-6.) 



Professor J. Arthur Thomson ^ in the first of 

 the following passages clearly states the germinal 

 origin of fluctuations, in the second correctly 

 expresses de Vries's conclusions : — 



(1) ' . . . when we collect a large number of specimens of 

 the same age from the same place at the same time, we 

 often find that no two are exactly alike. They have peculi- 

 arities of germinal origin— or, in other words, they show 

 individual or fluctuating variations.' (p. 78.) 



(2) 'Fluctuations do not lead to a permanent change in 

 the mean of the species unless there be a very rigorous 

 selection, and even then, if the selection be slackened, there 

 is regression to the old mean : mutations lead per saUum to 

 a new specific position, and there is no regression to the old 

 mean.' (p. 98.) 



I have brought perhaps unnecessarily ample 

 evidence in support of the fact that de Vries's 

 * fluctuations ' are assumed by him to be trans- 

 missible by heredity, and that this assumption is 

 an essential element in the author's definition of 

 his technical term. When we remember that 

 they are just the ' individual differences ' of 

 Darwin, and that de Vries's belief in their power- 

 lessness for continued evolution is based on Francis 

 Galton's well-known law of recession, it is really 

 waste of time to inquire whether they are trans- 

 missible. But such positive statements to the 

 contrary have been made by the most prominent 



' Heredity, Loudon, 1908. 



