MUTATION 307 



stitute a new race or a new variety, continuous because 

 of those insignificant gradations, of those numberless 

 transitions between individuals. It is also called Dar- 

 winian variation, because the characters created by this 

 variation determine, according to Darwin, the indi- 

 vidual's survival or disappearance in the struggle for 

 life. 



Those variations are almost universally observable. 

 They are taken into account by breeders and horticul- 

 turists who select individuals presenting the most de- 

 sirable characteristics in the highest degree and allow 

 them to breed to the exclusion of all others. One can 

 also list among slow variations those due to climate, 

 mode of life and nutrition. They are therefore the 

 basis of the Lamarckian theories as well as of all the 

 Darwinian theories. 



Besides this mode of variation there is another mode 

 designated as sudden or discontinuous mode. It com- 

 prises the modifications which appear suddenly and 

 are noticeable enough to be regarded as "anoma- 

 lous. The new character they impart to individuals is 

 not necessarily salient: the difference between the in- 

 dividual thus varied and the normal may not be any 

 greater than that which separates the two extremes 

 in fluctuating variations. What distinguishes this 

 mode of variation, however, is the absence of transi- 

 ; tional forms. The result is that the characters of 

 one species or of one variety may be suddenly modi- 



