Heredity and the Origin of Variations. 145 



continuity, for there is a continuity of the germinal cells, 

 the bearers of heredity. But how, it may be asked, on 

 this view, or on any continuity hypothesis, are the origin 

 of variations and their transmission to be accounted for ? 

 To this question we have next to turn. But before doing 

 so, it will be well to recapitulate and summarize the positions 

 we have so far considered. 



We saw at the outset that the facts we have to account 

 for are those of heredity with variation. To lead up to the 

 facts of sexual heredity, we considered fission, the regenera- 

 tion of lost parts, and budding in the lower animals. We 

 saw that, if a hydra be divided, each portion reproduces 

 appropriately the absent parts. But we found it difficult 

 to say whether this power resides, in such cases, in the 

 cells along the plane of section or in the general mass of 

 cells which constitute the regenerating portion. 



Having led up to the sexual mode of reproduction, we 

 inquired whether the egg produces the hen or the hen pro- 

 duces the egg. We saw that there is a marked difference 

 between a direct continuity of reproductive cells, giving rise 

 to body-cells as by-products, and an indirect continuity of 

 reproductive cells, these cells giving rise to the hen, and 

 then the hen to fresh reproductive cells, which, on this 

 view, are to be regarded as concentrated essence of hen. 



Darwin's hypothesis of pangenesis as exemplifying the 

 latter view was considered at some length, and the modi- 

 fications suggested by Professor Brooks, Mr. Galton, and 

 Professor Herdman were indicated. The hypothesis, so far 

 as it is regarded as a theory of the main facts of heredity, 

 was rejected. 



It was then pointed out that only in a few cases has a 

 direct continuity of germinal cells as such been actually 

 demonstrated. Whence Professor Weismann has been led 

 to elaborate his doctrine of the continuity of germ-plasm. 

 This germ-plasm can give rise to, but cannot originate 

 from, body-plasm. It may lurk in body-cells, which may, 

 by its subsequent development, be transformed into germ- 

 cells. But any external influences which may affect these 



