VI.] 



THEIR SIGNIFICANCE IN HEREDITY, 



369 



ancestral germ-plasms, a reduction which is repeated in every 

 generation. 



This must be so : the onl}^ question is, how and when does 

 the supposed reduction take place. 



Father. Mother. Offspring. 



eneration I. 



Generation II. 



III. 



HI. 



IV, 



IV 



Fig. I. 



Inasmuch as the germ-plasm is seated, according to our 

 theory, in the nucleus, the necessary reduction can only be 

 produced by nuclear division ; and quite apart from any ob- 

 servation which has been already made, we may safely assert 

 that there must be a form of nuclear division in which the an- 

 cestral germ-plasms contained in the nucleus are distributed to 

 the daughter-nuclei in such a way that each of them receives 



Bb 



