WEISMANN' S THEORY OF THE GERMPLASM 21 



nuclearplasms of certain series of cells. For these 

 reasons, ova and spermatozoa can arise only when 

 the germplasm which has been handed on from 

 the original nucleus to certain cells is able to over- 

 come the histogenous plasm of these cells. In this 

 respect Weismann has amended his original propo- 

 sition that the germ-cells were immortal, like 

 unicellular organisms. In a strict and literal inter- 

 pretation such a proposition would be incorrect, for 

 the germ-cells are immortal only so far as they 

 contain the germplasm, the immortal part of the 



organism. 



In its further elaboration Weismann's conception 

 was influenced considerably by publications of 

 Naegeli, De Tries, and Wiesner. These dealt with 

 the composition of the hereditary material, and 

 they contained new hypotheses concerning the 

 primary structure of the cell-body. Weismann 

 avowedly accepted the suggestion of De Yries, who 

 had rehabilitated and modernized Darwin's doctrine 

 of pangenesis, according to which gemmules, small 

 particles endowed with the power of division, were 

 the material bearers of hereditary characters. 



From these different sources Weismann has now 

 worked out, in minutest detail, a theory to which 

 he considers his former writings but as the preface ; 

 none the less, he has taken from his own writings 

 the most essential and characteristic sequences of 

 idea, in a fashion but slightly modilied. Let me 

 give the most important parts of his conception. 



The substance which is the bearer of the here- 

 ditary character of a species (the idioplasm of 



