22 An Examination of Weismannism. 



as in the previous case. So that, on the whole, we may 

 say that natural selection is ever waiting and watch- 

 ing for such combinations of germ-plasm as will give 

 the resulting organisms the best possible chance in 

 their struggle for existence; while, at the same time, 

 it is remorselessly destroying all those combinations 

 of germ-plasm which are handed over to the custody of 

 organisms not so well fitted to their conditions of life. 



It only remains to add that, according to Weis- 

 mann's theory in its strictly logical form, combinations 

 of germ-plasm when once effected are so stable that 

 they would never alter except as a result of entering 

 into new combinations. In other words, no external 

 influences or internal processes can ever change 

 the hereditary nature of any particular mixture of 

 germ-plasm, save and except its admixture with 

 some other germ-plasm, which, being of a nature 

 equally stable, goes to unite with the first in equal 

 proportions as regards hereditary character. So that 

 really it would be more correct to say that any given 

 mass of germ-plasm does not change even when it 

 is mixed with some other mass — any more, for in- 

 stance, than a handful of sand can be said to change 

 when it is mixed with a handful of clay. 



Consequently, we arrive at this curious result. 

 No matter how many generations of organisms there 

 may have been, and therefore no matter how many 

 combinations of germ-plasm may have taken place 

 to give rise to an existing population, each existing 

 unit of germ-plasm must have remained of the same 

 essential nature or constitution as when it was first 

 started in its immortal career millions of years ago. 

 Or, reverting to our illustration of sand and clay, the 



