4o6 Weismann's Theories — 



occurring very different instinctive actions of different 

 periods of life, as in this Sitaris and a multitude of 

 similar forms. All this, he tells us, is to be explained 

 exclusively by a mechanical arrangement of particles in 

 the germ. Now Professor Weismann, in criticising Nageli's 

 hypothesis, which would explain heredity by * conditions of 

 tension and movement,' declares (p. 182) that ' it would be 

 hardly possible to form even one approximate conception* 

 of such an explanation. We confess to being in the very 

 same position with respect to Professor Weismann himself. 

 We do not believe that such an arrangement of particles 

 as he supposes is a possible one — namely such an arrange- 

 ment of particles in the germ as to enable mere shock 

 and impact to produce all the phenomena of the life of 

 a creature of a certain kind; including all pathological 

 modifications and all instinctive actions. Such an hypo- 

 thesis makes greater demands on our credulity than does 

 even the now discredited theory of Pangenesis itself. 



Professor Weismann is an enthusiastic Darwinian, and 

 carries the principle of natural selection to much greater 

 lengths than it was carried by the venerable naturalist 

 who (with Mr. Wallace) promulgated it. Our judgment 

 concerning that principle has been expressed without 

 ambiguity,^ and to that judgment Ave firmly adhere. We 

 shall therefore enter into no further controversy on the 

 subject now, though we are compelled to notice certain of 

 Professor Weismann's references to it. He would explain 

 all adaptive phenomena and every specific origin exclusively 

 by the preservation through natural selection of accidental 

 differences in the disposition of particles within the germ, 

 excluding all direct action on progeny, through modifica- 

 tions induced by the environment in the soma of their 

 parents — a conception which of course very heavily handi- 



^ See ante, pp. 1-102. 



