240 THE GERM-PLASiM 



accompanying diagram (Fig. 19). (The boundaries between the 

 single ids are only indicated in generation IV. in the figure.) In 

 the second generation four groups, each consisting of four 

 similar ids, would be combined; in the third, eight groups of 

 two ids : and in the fourth, sixteen groups, each consisting of 

 only one id. The accompanying diagram illustrates this proc- 

 ess : the two parental idants are shown on the left, and their 

 fusion to one idant in the offspring on the right. The different 

 kinds of shading and dotting indicate the individual differences 

 between the ids. 



The minghng of the ids in the individual idants, just as in the 

 case of the mingling of the idants themselves, will not have 

 occurred so quickly and regularly as is indicated in the diagram : 

 but the final result is the same, whether the process takes place 

 more quickly or more slowly. 



The introduction of sexual reproduction will thus have gradu- 

 ally resulted in a greater degree of complication of the germ- 

 plasm, so that it is no longer composed of similar ids, but is 

 mainly made up of ids which are individually different from one 

 another^ All those phenomena of heredity which are spoken of 

 as the interfningling of the characters of ancestors^ such as 

 degeneration or atavisjn of all kinds and degrees^ depend^ I 

 believe^ on this complicated structure of the germ-plasm. 



In the following chapter an attempt will be made to explain 

 these phenomena theoretically. It will, however, first be neces- 

 sary to glance for a moment at the process of the reduction of 

 the ids, as far as we are acquainted with it. 



2. Proof that the Essential Part in the Process of 

 'Reducing Division' consists in the Extrusion of Ids 



In the chapter on the architecture of the germ-plasm, it was 

 pointed out that the ids are probably identical with the ' micro- 

 somes ' which are known to exist in many cases in the nuclear 

 rods, and not with the entire rods, or idants. This conjecture 

 was based on the fact that the rod-like chromosomes, the struc- 

 ture of which we are best acquainted with, consist of a series o^ 

 granules, or microsomes, which are separate and independent 

 structures. The composition of these rods evidently excludes 

 the possibility of considering each of them to be equivalent to a 

 single id. For an id is a vital unit, with a definite structure, and 



