WEISMANN'S CONCESSIONS. 179 



trate tissues througli wliicli even biophors can not pass ; and Prof. 

 Weismann, in showing tliat tlie latter must break out of jail, 

 sliould also explain how the former are able to break into jail. 

 Taking all these things into account, I am constrained to repeat a 

 former remark, that " if the term ' acquired ' is to be any further 

 refined away, then discussion is useless, for it is not a mere dis- 

 pute about a word that interests us, but the fundamental question 

 whether external conditions do or do not permanently and pro- 

 gressively influence the development of organic beings." * 



Reverting, then, to the main question as to the influence of 

 external conditions on the germ, I would remind the reader that 

 in his essay on amphimixis, originally published in 1891, Prof. 

 Weismann held that " a belief m the inheritance of acquired char- 

 acters by the highly differentiated Protozoa, as ivell as by Metazoa, 

 must be opposed," and imagined that " the phyletic modifications 

 of Protozoa arise from the germ-plasm, that is from the idioplasm 

 of the nucleus " ; f and he further says : 



" My earlier views on unicellular organisms as the source of 

 individual differences, in the sense that each change called forth 

 in them by external influences, or by use and disuse, was supposed 

 to be hereditary, must therefore be dismissed to some stage less 

 distant from the origin of life." | 



He then ascribed all variations above this early stage to am- 

 phimixis and sexual reproduction. In the new work he indeed 

 reiterates this view, and says that these processes furnish "an 

 inexhaustible supply of fresh combinations of individual varia- 

 tions which are indispensable to the process of selection." * But 

 he now introduces the following important qualification : 



" Although the process of amphimixis is an essential condition 

 for the further development of the species, and for its adaptation 

 to new conditions of existence among the higher and more com- 

 plicated organisms, it is not the primary cause of hereditary vari- 

 ation." II 



He then proceeds to explain the change that has taken place in 

 his mind, obviously while writing this book, admits that he had 

 overestimated the power of sexual reproduction to modify spe- 

 cies, and shows that though the general result might be changed 

 there could be no variation in the determinants themselves, 

 " which alone could gradually lead to a transformation of the 

 species." Not only is amphimixis incapable of modifying the de- 

 terminants, but it is also, and for the same reason, incapable of 

 increasing the number of kinds, yet on his general theory these 



* Neo-Darwinism and Neo-Lamarckism, etc., p. 59. 



f Essays, vol. ii, p. 192. X ^^'^^-i P- l^'^- 



* The Germ-Plasm, p. 413. || Ibid., p. 414. 



