PART I. 



WEISMANN'S THEORY OF THE GERMPLASM 

 AND DOCTRINE OF DETERMINANTS. 



As may be seen in his essays, On Life and Death, 

 On the Duration of Life, etc., Weismann believes 

 himself to have established a fundamental dis- 

 tinction between unicellular and multicellular 

 organisms. Unicellular organisms (he would have 

 it) do not undergo natural death, but, since they 

 are able to reproduce themselves continuously 

 by a process of simple division, are immortal. 

 Multicellular organisms, on the other hand, must 

 perish after a definite duration of life, and so are 

 mortal. He makes an exception of the sexual 

 cells, which, like unicellular organisms, are able to 

 multiply indefinitely, and so are immortal. Thus 

 Weismann came to make a distinction between the 

 mortal (somatic) cells and the immortal (germ) cells 

 of multicellular organisms. The latter he regarded 

 as arising directly from the egg-cell, and never 

 from somatic cells. 



Nussbaum has given utterance to similar views, 

 holding that the dividing egg at a very early period 

 cleaves into the cells from which the individual 



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