THEORIES OF HEREDITY 63 



kind of determinant is left for the final cells of the body. 

 Only one kind of determinant is destined for each kind of 

 cell, be this cell temporary or permanent. The influence of 

 the determinants on the cell-body is due to their final 

 disintegration into the " Biophors," the smallest living 

 particles of which they are composed. These, which are 

 characteristic for each kind of determinants, leave the 

 nucleus, enter the cell-body, and impress on the morpho- 

 plasm of the cell the appropriate character. 



Just as the formation of the normal cells, organs, etc., 

 of the body is due to the presence of a special kind of 

 determinant, so does Regeneration, according to Weis- 

 mann's view, also depend on the right kind of determinants 

 being present at the place of regeneration. These deter- 

 minants must exist as " adventitious germ-plasm " in a 

 latent state, wherever regeneration is possible, until 

 occasion arises for them to become active. In such cases, 

 as in a divided worm, where both ends may regrow the 

 missing portions of the body, it is, of course, necessary to 

 assume that at the plane of partition two sets of determin- 

 ants are present, those for the fore-parts and those for 

 the hind-parts of the body, and that each kind becomes 

 active, according to which part of the animal has to be 

 regenerated. 



Many fundamental objections have been raised against 

 Weismann's system of determinants, which it would be 

 impossible to deal with here. Professor Delage, a French 

 scientist, goes perhaps farthest in denying the necessity of 

 any kinds of units. He thinks he can explain all the 

 various phenomena of heredity, etc., by the interaction 

 of forces between the physico-chemical constitution of the 

 living germ and external conditions, just as we get by the 

 reaction between water and different physical forces its 

 various forms of rain, snow, hail, river, etc. 



Oscar Hertwig, who does not accept determinants for 

 any other characters of the body than actual cell-qualities, 

 attributes characters determined by groups of cells (as 



