>} VARIATION 411 



as that which gave rise to the copper-beech in the 16th cen- 

 tury, or to hornless cattle, or to short-legged sheep, or to 

 Angora rabbits, or to fantail pigeons. They correspond to 

 Galton's " transilient variations ", to Bateson's " discontinu- 

 ous variations ", to De Vries's " mutations ", and the last 

 name should be kept for them. The contrast, it should be 

 noted, is not so much in the amount as in the kind of change. 

 A white rat does not seem to lack very much to make it a 

 brown rat the species whence it sprang, but it was in its 

 day a qualitative new departure, and it has bred true. (&) 

 By " individual variations " Darwin meant the minute, 

 ubiquitous peculiarities which distinguish child from parent, 

 brother from brother, cousin from cousin. Though he was 

 much interested in the " single variations " or brusque 

 " sports ", it was in "individual variations" or minute 

 fluctuations that he found most of the raw materials of new 

 species. " The more I work," he said, " the more I feel 

 convinced it is by the accumulation of such extremely slight 

 variations that new species arise." 



Some authors have tried to identify Darwin's slight in- 

 dividual variations or fluctuations with the somatic modi- 

 fications already referred to. While this may be sometimes 

 justified in point of fact, Darwin did not regard minute 

 variations as modificational. This is plain from such a 

 sentence as this: "If, as I must think, external conditions 

 produce little direct effect, what the devil determines each 

 particular variation?" Moreover, fluctuations or minute 

 variations often arise among animals whose conditions of 

 life appear to be quite uniform. On the other hand, what 

 Johanssen calls fluctuations in " pure lines " of beans are 

 probably slight modifications due to differences in nurture. 

 Little is known in regard to the transmissibility of 



