6S THE GERM-PTASM 



which they arose, the ids produced by the division naturally 

 contain precisely similar determinants ; in embryogeny, on the 

 other hand, divisions occur which ensure that the two dauirhter- 

 nuclei contain combinations of determinants which are usually 

 entirely different from one another. We have an example of 

 such a nuclear division in the segmentation of the ovum in the 

 case, for instance, of certain worms already referred to, in which 

 two cells are formed by the first division of the egg-cell, one of 

 which contains all the determinants of the internal, and the 

 other all those of the external germinal layer. A division of 

 this latter kind we may speak of as differ e)itial or dissimilar 

 as regards heredity (' erbungleich '), in contrast to the former, 

 which is integral or similar as regards heredity (^ erbgleich ^) . 

 As in the case of the entire idants, the ids are split by an inter- 

 nal force, and are not pulled apart mechanically by the threads 

 of the ' nuclear spindle ' which are attached to them. Flemming 

 has shown that this splitting often takes place long before the 

 spindle-threads become active. The forces of attraction in the 

 determinants must therefore take part in this process, just as they 

 must be assumed to act between the biophors which constitute 

 the body of a dividing cell. 



It appears to me, therefore, that the inherited architecture of 

 the id of germ-plasm undergoes a gradual change, owing to the 

 uneven rate of multiplication of the determinants, and that it 

 is further regulated by the forces of attraction which we must 

 suppose to act between them. We might represent the archi- 

 tecture of the id by a very complicated geometrical figure, which 

 gradually becomes changed during the growth of the id ; this 

 change does not occur in the first division, the preparation for 

 which has been accurately made in the original figure, but in 

 the subsequent stages of ontogeny. As the greater number 

 of these divisions is connected with a diminution in the number 

 of kinds of determinants, the geometrical figure representing 

 the id gradually becomes simpler and simpler, until finally it 

 assumes the simplest conceivable form, and then each cell will 

 contain the single kind of determinant which controls it. The 

 disintegration of the germ-plasm is a wonderfully complicated 

 process ; it is a true ' development,' in which the idic stages 

 necessarily follow one another in a regular order, and thus the 

 thousands and hundreds of thousands of hereditary parts are 

 gradually formed, each in its right place, and each provided with 

 the proper determinants. 



