200 HOLISM AND EVOLUTION chap. 



bread cast on the waters of destiny, to be lost utterly, or 

 to be found after many days. But the past and the future 

 of the race dwelt sublime and secure in the eternal sanctuary 

 of the germ-cell. 



Such was the great Weismann conception, which in effect 

 largely withdrew creative Evolution from the arena of exter- 

 nal conflict and the mechanical struggle for existence, and 

 located its origins in the secluded depths of the inner world 

 of the germ-cell. And this great conception was based on 

 Weismann's view of the mechanism of the germ-cell, on 

 which a great deal of light has since been thrown by experi- 

 mental research and observation. 



Without going into details we may just note that the 

 chromosomes of the dividing nucleus have been identified 

 as on the whole the carriers of the hereditary characters of 

 organisms; these characters have to some extent been cor- 

 related with distinct chromosomes, and the number, shape, 

 size and other differences of chromosomes in the nucleus 

 of the germ-cell are therefore taken to be the physical 

 basis of the characters which distinguish the species. It 

 has been found necessary to go further and to assume in 

 the chromosomes themselves active elements or factors or 

 genes which are productive of organic characters. These 

 researches and speculations are still in their initial stages, 

 but they are important and have this advantage, that the 

 results of intercrossing and hybridising in producing a 

 change of characters can be studied in conjunction with the 

 simultaneous change in number and form of chromosomes. 

 In the prosecution of experimental Evolution the parallelism 

 of cell structure and of variation in organic characters thus 

 supplies a double weapon of attack. 



While the germ-cell as the mechanism of heredity is easily 

 understood, the question still remains how it operates as 

 the sole and independent cause of Variation. The inter- 

 mixture of chromosomes from two separate individuals in 

 sexual reproduction, and the changes in the chromosome 

 contents of the reproductive cells in their previous meiotic 

 division, undoubtedly provide the occasion for a great inter- 



