292 THE WHENCE AND THE WHITHER OF MAN 



adult individuals, composed mainly of somatoplasm. 

 Or we may imagine a long chain, with a pendant at- 

 tached to each tenth or one-hundredth link. The links 

 of the chain would represent the series of generations 

 of germ-cells ; the pendants, the adults of successive 

 generations. 



But any leaf of begonia can be made to develop 

 into a new plant, giving rise to germ-cells. Here there 

 must be scattered through the leaves of the plant small 

 portions of germ-plasm, which generally remain dor- 

 mant, and only under special conditions increase and 

 give rise to germ-cells. 



A large part of the germ-plasm of the fertilized egg 

 is used to give rise to the somatoplasm composing the 

 different systems of the embryo and adult. Weis- 

 mann's explanation of this change of germ-plasm into 

 somatoplasm is very ingenious, and depends upon his 

 theory of the structure of the germ-plasm ; and this 

 latter theory forms the basis of his theory of evolution. 

 It would take too long to state his theory of the 

 structure of germ - plasm, but an illustration may 

 present fairly clear all that is of special importance 

 to us. 



The molecules of germ-plasm are grouped in units, 

 and these in an ascending series of units of continu- 

 ally increasing complexity, until at last we find the 

 highest unit represented in the nucleus of the germ- 

 cell. This grouping of molecules in units of increasing 

 complexity is like the grouping of the men of an army 

 in companies, regiments, brigades, divisions, etc. 



To form the somatoplasm of the different tissues of 

 the body, this complicated organization breaks up, as 

 the egg divides, into an ever-increasing number of cells. 



