i 4 MENDELISM chap. 



theory of heredity which eventually appeared in his work 

 on The Germplasm (1885), a book which will be remem- 

 bered for one notable contribution to the subject. Until 

 the publication of Weismann's work it had been generally 

 accepted that the modifications brought about in the 

 individual during its lifetime, through the varying 

 conditions of nutrition and environment, could be trans- 

 mitted to the offspring. In this biologists were but fol- 

 lowing Darwin, who held that the changes in the parent 

 resulting from increased use or disuse of any part or or- 

 gan were passed on to the children. Weismann's theory 

 involved the conception of a sharp cleavage between the 

 general body tissues or somatoplasm and the reproductive 

 glands or germplasm. The individual was merely a car- 

 rier for the essential germplasm whose properties had 

 been determined long before he was capable of leading 

 a separate existence. As this conception ran counter to 

 the possibility of the inheritance of " acquired charac- 

 ters," Weismann challenged the evidence upon which it 

 rested and showed that it broke down wherever it was 

 critically examined. By thus compelling biologists to 

 revise their ideas as to the inherited effects of use and dis- 

 use, Weismann rendered a valuable service to the study 

 of genetics and did much to clear the way for subsequent 

 research. 



A further important step was taken in 1895, when Bate- 

 son once more drew attention to the problem of the origin 



