SUMMARY OK TART II 225 



CHAPTER VII 



Summary of Part II 



We have now seen that the idioplasm of the fully-formed in- 

 dividual animal- or plant-cell may exhibit a considerable amount 

 of difference as regards its degree of complexity ; and before 

 going further, it may be as well to state clearly in what this 

 difference consists. 



We suppose that the process in the idioplasm which brings 

 about the ontogeny of a multicellular organism is due to the 

 thousands of determinants, which constitute the germ-plasm ot 

 the fertilised ovum, becoming systematically separated into 

 groups, and distributed among the successors of the egg-cell. 

 This separation into smaller and smaller groups of determinants 

 continues to take place, until each cell contains determinants 

 of one sort only, and these then either control a single cell, or, 

 in case the hereditary character (* determinate ') is constituted 

 by a group of cells with a common origin, the control is exerted 

 over this whole group. 



All the determinants are not active at the same time ; every 

 cell, in fact, which appears in the entire course of ontogeny is 

 controlled by one determinant. This is effected by the disin- 

 tegration of the detcminant into its constituent biophors, which 

 migrate into the cell-body. Even in the earlier stages of ontog- 

 eny, in which the idioplasm of a cell consists of a still larger 

 number of different kinds of determinants, the cell is also con- 

 trolled by only one of them in this manner. The rest of the 

 determinants have in any case an important function with regard 

 to the course taken by ontogeny, for each of them has its own 

 rate of increase, and thus an alteration is produced in the pro- 

 portion of the various determinants originally present in the 

 germ-plasm, and consequently its definite architecture also 

 undergoes alteration, the subsequent disintegration being con- 

 trolled by the determinants which have thus been rearranged. 

 These determinants are therefore only inactive with respect to 



