28 THE BIOLOGICAL PROBLEM OF TO-DAY 



series of cells, a quantity of accessory, or bud, 

 idioplasm. 



The phenomena of alternation of generations 

 require the supposition that in those animals and 

 plants in which it occurs ' two kinds of germplasm 

 exist, both of which always are present in the egg 

 or in the bud, but of which one only is active at 

 any time and rules the ontogeny, while the other 

 remains inactive.' The alternating activity of these 

 two produces the alternation of generations. So 

 also dimorphism, which is exhibited most frequently 

 as differences between the sexes, is explained by 

 the assumption that ' double determinants ' are 

 present in the germplasm for all the cells, cell- 

 groups, or entire organisms which have different 

 characters in the male and female. One set of 

 these double determinants remains latent, the other 

 becomes active. 



Finally, to explain the phenomena of regenera- 

 tion, it is assumed that in the complicated cases 

 where large parts of the body, like the head, the 

 tail, or a bone, can be replaced after accidental 

 loss, the cells with this power of regeneration con- 

 tain, in addition to the determinants proper to 

 them, supplementary determinants, which contain 

 the germs needed for regeneration of the lost parts. 

 These were handed on, during the ontogeny, 

 through definite series of cells, in a passive con- 

 dition, to become active when the conditions for 

 their growth are supplied by the loss of the parts 

 they can replace. 



