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SCIENCE. 



[N. S. Vol. IV. No. 99. 



criticism. The problems of heredity were 

 recognized as being of supreme biological 

 importance and were warmly discussed. 

 Meanwhile a diflferent view of the relation 

 between the organism and its reproductive 

 cells came into prominence. "With it the 

 names of Francis Galton, in England, and 

 August Weismann, in Germany, are insep- 

 arably connected. Of late years it has 

 gained the approval of many, though by no 

 means all, of our foremost biologists. This 

 view, again given in briefest possible out- 

 line, is as follows : The fertilized egg of any 

 many- celled organism gives origin to all 

 the cells of which that organism is com- 

 posed. In some of these, the reproductive 

 cells, germinal substance is set aside for 

 the future continuance of the race; the rest 

 give rise to all the other cells of the body, 

 those which constitute or give rise to 

 muscle, nerve, bone, gland and so forth. 

 Thus we have a division into germ-sub- 

 stance and body-substance. Germ gives 

 origin to germ plus body ; but the body 

 takes no share, according to Prof. Weis- 

 mann, in giving origin to — though it min- 

 isters to, protects, and may exercise an in- 

 fluence on — the germinal substance of the 

 reproductive cells. 



The logical development of this theory 

 led Prof. Weismann to doubt the inherit- 

 ance of characters acquired by the bodily 

 substance in the course of individual life, 

 and to examine anew the supposed evidence 

 in its favor. For if brain substance, for 

 example, contributes nothing to the repro- 

 ductive cells, any modification it acquires 

 during individual life can only reach the 

 germ through some indirect mode of influ- 

 ence. But does it — does any modification 

 of the body substance — so afiect the germ 

 as to become hereditary? Prof. Weismann 

 answers this question by asserting that the 

 evidence for the direct transmission of ac- 

 quired characters is wholly insufficient, and 

 by contending that, until satisfactory evi- 



dence is forthcoming, we may not accept 

 transmission as a factor in evolution. 



How, then, is progress possible if none of 

 the modifications which the body sufiers is 

 transmitted from parent to offspring? To 

 this question we must reply that though 

 modification is, on this view, excluded from 

 taking any direct share in race- progress, 

 yet there is still variation. By modifica- 

 tions I mean those changes which are in 

 some way wrought in the body- structure, 

 and by variations those differences which 

 are of germinal origin. That variation of 

 germinal origin is a fact in organic nature 

 is admitted on all hands, and that some 

 variations are adaptive is also unquestioned. 

 Transmissionists contend that modification 

 in a particular direction in one generation 

 is, through the transmission of the change 

 in some way from the bodily tissues to the 

 germinal cells, a source of variation in the 

 same direction in the next generation. Se- 

 lectionists, on the other hand, exclude this 

 source of variation, contending that the 

 supposed evidence in its favor is insufficient 

 or unsatisfactory. But their whole theory 

 depends on the occurrence of variations, of 

 which those that are in unfavorable direc- 

 tions are weeded out, while those that are 

 useful and adaptive remain in possession of 

 the field. How these variations originate 

 in the germ we need not here (discuss. Let 

 us assume that variations of germinal ori- 

 gin in a great number of directions do as a 

 matter of fact occur. 



This, then , is how the matter stands . All 

 acknowledge the existence of variations and 

 admit that their proximate source is in the 

 fertilized ovum. All admit that the indi- 

 vidual is, through its plasticity, in greater 

 or less degree capable of adaptive modifica- 

 tion. Transmissionists contend that the 

 effects of modification are somehow trans- 

 ferred to the germinal substance there to 

 give origin to variations. Selectionists deny 

 this transmission and contend that adap- 



