X OBITUARY NOTICES OF MEMBERS DECEASED. 



changes of the germ-plasm led to general and unpredictable changes 

 in future generations which might be wholly different from those 

 somatic changes in the parents which were directly produced by such 

 environment. This view is now widely accepted. 



Thus while Weismann's views on this subject underwent cer- 

 tain changes in the course of his long life, the opinions of his 

 opponents have undergone so much greater and more important 

 changes that it may be truly said that in the matter of the inheri- 

 tance or non-inheritance of acquired characters the greater portion 

 of the scientific world has come to Weismann's position. 



Finally mention must be made of Weismann's theory of evolu- 

 tion which was a direct outgrowth of his theory of heredity. He 

 maintained that evolution must depend upon an evolution of the 

 germ-plasm and that this was brought about chiefly, if not entirely, 

 by the mixture of different kinds of germ-plasms (amphimixis) in 

 the union of the sex cells. There is no doubt that many variations 

 are produced by amphimixis but in general these combinations of 

 germ-plasms are not actual fusions ; new combinations of inheri- 

 trance units are produced but not new units, and usually these new 

 combinations split up in subsequent generations according to Men- 

 delian rules, so that such temporary combinations of different germ- 

 plasms do not usually lead to permanent modification, or to evolu- 

 tion, of the germ-plasm. On the other hand it is probable 

 that Weismann underestimated the possible influence of environ- 

 ment in producing changes in the germ-plasm and hence its in- 

 fluence on evolution ; at least it does not seem possible at present 

 to explain the origin of many inherited mutations except by the 

 influence of changed environment upon the developing germ cells. 



In his belief in Natural Selection Weismann out-Darwined 

 Darwin or any of the Darwinians. Darwin dealt only with the 

 survival of individuals or races in the struggle for existence and 

 was always inclined to assign a good deal of weight to the influence 

 of environment in producing new races. Weismann would not 

 admit the existence of any other factor of evolution than selection 

 and he extended this principle from individuals or persons ("per- 

 sonal selection") to organs and tissues ("histonal selection") and 



