TRANSLATOR'S INTRODUCTION xi 



from the first division of the germplasm that we 

 are concerned here. It is set apart to form the 

 nuclear matter, and so to control the building up 

 of the actual individual. Weismann supposes that 

 the subsequent divisions it undergoes are what I 

 call in this translation differentiating divisions 

 (Erbungleiche Theilung). According to his theory, 

 in each of these divisions the microcosms of the 

 germplasm are not doubled, but are slowly dis- 

 integrated, the division differentiating among the 

 determinants, and marshalling one set into one 

 portion, the other set into the other portion. The 

 differentiating process occurs in an order deter- 

 mined by the historic architecture of the micro- 

 cosms, so that the proper determinants are liberated 

 at the proper time for the modelling of the tissues 

 and organs. Ultimately, when the whole body is 

 formed, the cells contain only their own kind of deter- 

 minants. It follows, of course, from this that the 

 cells of the tissues cannot give rise to structures 

 containing less disintegrated nuclear material than 

 their own nuclear material, and least of all to 

 reproductive cells, which must contain the undis- 

 integrated microcosms of the germplasm. As 

 special adaptations for the formation of buds and 

 for the reconstruction of lost parts, cells may be 

 provided with latent groups of determinants to 

 become active only on emergency. But with these 

 exceptions, the nuclear matter of the cells of the 

 body contains only what is called idioplasm, a 

 differentiated portion of the germplasm peculiar to 

 cells of their own order, and it can give rise only to 



