238 THE GERM-PLASM 



affected every kind of idant to the same extent ; the germ- 

 plasm of the fourth generation would then consist of the idants 

 2A + 2B-I-2C+2D + 2E + 2F + 2G + 2H, and that of 

 the fifth, of a number of individually different idants, — provided, 

 of course, that interbreeding had not occurred. The germ-plasm 

 of this fifth generation would therefore consist of the idants A — Q. 



This naturally does not imply that the process would really 

 take place in such an even and systematic manner ; it must, on 

 the contrary, be a very irregular one. But although it may not 

 in five generations have resulted in the germ-plasm being com- 

 posed of a number of different ids, this result must certainly fol- 

 low in the course of a greater number of generations. 



The modification of the germ-plasm will not, however, then 

 have reached its limit. If my view of the composition of idants 

 out of ids is a correct one. and the id is really a unit w'hich con- 

 tains all the primary constituents of the species, — that is to say, 

 if it contains all the determinants required for the construction 

 of a single individual, — it follows that the composition of the 

 individual idants imist gradually have become changed, so that 

 each idant, instead of being made up of similar ids, comes to be 

 constituted by dissimilar and individually differ eiit ids. 



The idants are not, in my opinion, perfectly invariable quan- 

 tities ; certain phenomena of heredity have led me to conclude 

 that they are in any case only relatively constant, and that their 

 composition becomes modified from time to time, so that the 

 ids which previously belonged to the idant A may later take 

 part in the composition of the idant B or C. Our present knowl- 

 edge of the processes of the division of the nuclear substance 

 does not enable us to say how frequently and regularly this 

 occurs ; but even if it only takes place at irregular intervals, during 

 long periods of time, it must nevertheless have resulted in a very 

 varied composition of the idants in the course of the enormous 

 number of generations which have ensued since the introduction 

 of the process of amphimixis into the organic world. As new 

 idants are always added to those already present in one of the 

 parents each time amphimixis occurs, a continual interpolation 

 of new ids can take place in the idants ; and as this process is 

 repeated an indefinite number of times, a single idant must 

 ultimately — if we neglect the repetition of similar ids which 

 results from interbreeding — come to consist of a number of 

 individually different ids. 



