76 THE GERM-PLASM 



cell, or of a small or even large group of cells (^.g., blood-cor- 

 puscles) . 



These determinants control the cell by breaking up into bio- 

 phors, which migrate into the cell-body through the pores of the 

 nuclear membrane, multiply there, arrange themselves according 

 to the forces within them, and determine the histological struc- 

 ture of the cell. But they only do so after a certain definitely 

 prescribed period of development, during which they reach the 

 cell which they have to control. 



The cause of each determinant reaching its proper place in 

 the body depends on the fact that it takes up a definite position 

 in the id of germ-plasm, and that the latter, therefore, exhibits 

 an inherited and perfectly definite architecture. Ontogeny 

 depends on a gradual process of disintegration of the id of germ- 

 plasm, which splits into smaller and smaller groups of determi- 

 nants in the development of each individual, so that in place of a 

 million different determinants, of which we may .suppose the id 

 of germ-plasm to be composed, each daughter-cell in the next 

 ontogenetic stage would only possess half a million, and each 

 cell in the next following stage only a quarter of a million, and 

 so on. Finally, if we neglect possible complications, only one 

 kind of determinant remains in each cell, viz., that which has to 

 control that particular cell or group of cells. This gradual dis- 

 integration of the id of germ-plasm into smaller and smaller 

 groups of determinants in the subsequent idic stages does not 

 consist in a mere division of the id into portions, but — as occurs 

 in all disintegrations of vital units — is accompanied by dis- 

 placements in the groups of these units, brought about by the 

 unequallv vigorous multiplication of the various individual deter- 

 minants, and regulated by the forces of attraction acting within 

 them, /n spite of all the alterations in the arrangement of the 

 determinants which must occur, owing to the diiTerential nuclear 

 divisions together with unequal growth of the various kinds of 

 these units of the second order, the original position of each 

 determinant in the extremely complex structure of the id of 

 germ-plasm renders it necessary that it should take up a definite 

 and fixed position in each idic stage ; and also that it should 

 traverse the precisely regulated course from the id of germ- 

 plasm, through perfectly definite series of cells, to the cell in 

 which it reaches maturity in the final stage of development. In 

 this cell it breaks up into its constituent biophors, and gives the 



