Weismanns theory of Heredity (1891). 67 



hereditary individual variations may be produced by 

 other causes, and Weismanns theory of evolution 

 collapses. Therefore, if we are to examine his 

 theory of evolution^ we can do so only by ignoring 

 such a passage as the one just quoted, which sur- 

 renders the postulate of the absolute stability of germ- 

 plasm. 



Again, if we are to examine Weismann's theory of 

 heredity, we must similarly ignore such a passage as 

 the following, where he represents that he is similarly 

 prepared to surrender his still more fundamental 

 postulate of the perpetual continuity of germ-plasm. 



After remarking that some of his own experiments 

 on the climatic varieties of certain butterflies raise 

 such difficulties against his whole theory of heredity 

 that even now he (i cannot explain the facts otherwise 

 than by supposing the passive acquisition of characters 

 produced by the direct influence of climate," he goes 

 on to remark more generally — "We cannot exclude 

 the possibility of such a transmission occasionally 

 occurring, for, even if the greater part of the effects 

 must be attributed to natural selection, there might 

 be a smaller part in certain cases which depends 

 on this exceptional factor 1 " — i.e., the Lamarckian 

 factor ! 



Now, it must be particularly noted that in this 

 passage Weismann is speaking, not as in the previous 

 passage, of sepcialized congenital characters, but of 

 representative congenital characters. In other words, 

 he here entertains the possibility which in the passage 

 previously quoted he very properly rejects — namely, 

 "that changes of the organism which result from 



1 Essays, &c, 2nd ed., p. 100. 

 F 2 



