132 OTHER FACTORS OF EVOLUTION 



but the corresponding variation evoked by the same external influence 

 in the relevant determinants of the germ-plasm within the germ-cells, 

 in other words, in the determinants of the following generation." 

 Elsewhere, also, he had previously said ' : — " Many climatic varia- 

 tions may be due wholly or in part, to the simultaneous variation of 

 corresponding determinants in some part of the soma and in the 

 germ-plasm of the reproductive cells." This double simultaneous 

 action seems first to have been suggested by Francis Galton in 1895, 

 though it was more definitely expressed later by Cope, who gave 

 to the process the name of ' Diplogenesis.' ^ 



Here we have surely the plainest admission from Weismann 

 himself of the very occurrence of the matter in dispute, that is, the 

 transmission of acquired variations. The thing itself is admitted to 

 occur, and it is a matter of altogether minor importance whose 

 hypotheses are capable of giving the best explanation of the mode 

 in which it is brought about. Formerly to satisfy Weismann the 

 change was regarded as primary in the germ-plasm, and owing 

 to nutritional variations therein. Thus, speaking of one of Hoff- 

 mann's experiments he says (" Essays," I, p. 426) : — " The body of 

 the plant — the soma — has not been directly affected by external 

 influences, in Hoffmann's experiments, but changes have been 

 wrought in the germ-plasm of the germ-cells and, only after this, 

 in the soma of succeeding generations . . . the idioplasm was 

 changed more and more in the course of generations, until at last 

 the change became great enough to produce a visible character in 

 the soma developed from it. Because in this, and in many other 

 cases a particular change did not " become visible until after some 

 generations had elapsed," Weismann here assumes that the change 

 must have been initiated in the germ-plasm itself. 3 But whether 

 that is true, and whether production of the new characters in plant 

 or animal must of necessity be initiated in the germ-plasm, anterior 



' " The Germ Plasm," Contempy. Sc. Series, 1893, p. 406 ; see also " Evolution," 

 II., p. 272. 



' " American Naturalist," Dec, 1889, published in 1890. 



3 On the other possibility some hints are given by Herbert Spencer in 

 " Biology," II., p. 620. Light is thrown upon such a process also by certain 

 experiments with the larvas of butterflies. Referring to them Cope (loc. cit. p. 440) 

 says : — "In another experiment, larvae which were in the act of weaving cocoons, 

 on exposure to certain colours, were induced to weave cocoons of corresponding 

 colours. This experiment demonstrates that a stimulus may be transmitted to a 

 gland so as to modify the character of its secretion in a new direction. . . . This 

 prepares us to look upon heredity as an allied phenomenon, i.e., the transmission 

 of a special energy from a point of stimulus to the germ-cells," 



