THE GERM-PLASM 59 



which live in the dark, the number of these setae is greater than 

 in the case of related forms which possess the sense of sight. 

 And though in all these instances individual deviations occur, 

 we may nevertheless suppose them to be hereditary, for other- 

 wise the increase in the number of olfactory setae incident on 

 a life in darkness, could not have been established as a specific 

 character. 



In smaller and simpler organisms each individual cell may 

 well have been determined from the germ onwards, and not 

 merely with the result that the number of cells is a definite one, 

 and the position of each definitely localised : the determination 

 may also have caused individual peculiarities of each cell, in so 

 far as they depend on changes in the germ-plasm at all — i.e.^ 

 are * blastogenic,^ — to reappear in the corresponding cell in the 

 next generation, just as in the case of a birthmark in the human 

 subject which recurs in precisely the same place on the same 

 side of the body. This may also be true of animals as simple as 

 the DicyeinidcB or the Tardigrada, although it is not possible to 

 prove it positively. 



In all the more highly differentiated animals there can be 

 little doubt that the number of determinants is always very much 

 less than that of the cells which are the factors in the process of 

 ontogeny. If we compare this statement with Darwin's assump- 

 tion of the presence of a gemmule — or rather of several gem- 

 mules — for each cell, it is evident that the germ-plasm is thus 

 to some extent relieved of a burden. 



We must not forget, however, that a cell may vary as regards 

 transmission not only as a whole but also in its parts, so that 

 not one but several biophors must be assumed for each deter- 

 minant of a cell or group of cells ; we must, in fact, suppose just 

 as many to be present as there are structures in the cell which 

 are variable from the germ onwards. We ought, properly speak- 

 ing, to speak of these bearers of qualities, which correspond to 

 de Vries's pangenes, as determinants also, for they determine 

 the parts of a cell. As the name of biophor has been given to 

 them, however, it is better to retain this term, and to define a 

 deter 7niiiant as a priinary constituent of a cell or group of cells. 

 Thus a determinant is always a group of biophors, and never a 

 single one. 



It may now, I believe, be proved without difficulty that the 

 biophors determining a cell not only lie close together in the 



