214 Two Kinds of Variation 



tion of the pangens in the cytoplasm of an individual cell 

 is only minimal. 



The giving off of the pangens by the nucleus must, as 

 a matter of course, always be done in such a way that all 

 kinds of pangens remain represented in the nucleus. Al- 

 ways only a relatively small number of like pangens must 

 leave the nucleus. The division of the nuclei, however, 

 must take place in such a way that all the different kinds 

 of pangens are evenly distributed over the two daughter- 

 cells. Only in certain somatarchic cell-divisions^^ is there 

 a deviation from this regularity. 



The two kinds of variability which Darwin distin- 

 guishes on the ground of pangenesis, are naturally also to 

 be deduced from the description here given.^^ Fluctuating 

 variability is simply based on the varying numerical rela- 

 tion of the individual kinds of pangens, which relation 

 can indeed be changed by their multiplication and under 

 the influence of external circumstances, but most quickly 

 by breeding selection. The "species-forming" variabil- 

 ity,^** that process by which the differentiation of living 

 forms has come about, in its main lines, must essentially 

 be reduced to the fact that the pangens, in their division, 

 produce, as a rule, two new pangens that are like the 

 original one, but that exceptionally these two new pangens 

 may be dissimilar. Both forms will then multiply, and 

 the new one will tend to exercise its influence on the visi- 

 ble characters of the organism. 



In harmony with this is the idea that we must imagine 

 the higher organisms to be composed of a greater number 

 of unlike pangens than the lower ones. 



i8Cf. pp. 102 and 107. 



i9Cf. p. 74. 



20N0W commonly called mutability (de V. 1909). 



