Later Additions tip to the year 1892. 31 



likewise contain nucleo-plasm in two kinds — one having 

 to do only with the formation and control of its own 

 individual cell, and the other having to do with the 

 formation of the future somatic-cells, which will have 

 to follow in the course of ontogeny. Therefore, in 

 order to designate this second kind of nucleo-plasm 

 (whether in a germ-cell or a somatic-cell) Weismann 

 borrows from Nageli the term " idio-plasm 1 ," or rather, 

 I should say, he uses the term " nucleo-plasm " when 

 he is speaking of all the contents of a nucleus indis- 

 criminately, while he uses the term " idio-plasm" when 

 he has occasion to speak specially of the two kinds of 

 nucleo-plasm now before us. 



Hence, the nuclear contents (nucleo-plasm) of every 

 cell, whether germinal or somatic, present two sub- 

 stances, which we may, in the absence of any better 

 terms supplied by Weismann himself, respectively 

 designate "idio-plasm- A" and "idio-plasm-B." Idio- 

 plasm-A is the substance which has to do only with 

 the formation and control of the individual cell in 

 which it resides,, like a mollusc in its shell. Idio- 

 plasm-B is the substance out of which future cells 

 are to be formed and controlled, when in due course 

 either of ontogeny or phylogeny this idio-plasm-B 

 becomes converted into idio-plasm-A, — i. e., into each 

 subsequently developing tissue or organism, as the case 

 may be. I say ontogeny or phylogeny, and tissue 

 or organism, because, where a germ-cell is concerned, 

 idio-plasm-B is capable of reproducing entire organ- 

 isms of its own and of subsequent generations; whereas, 



1 The meaning of this term, however, as originally used by Nageli, 

 he so greatly changes to suit the requirements of his own theory, that 

 I think it would have been better had he coined some new one. 



