114 EVOLUTION 



Why Like Tends to Beget Like. — The 

 fundamental hereditary relation is such that 

 like tends to beget like, and the reason for 

 this is found in the fact of germinal con- 

 tinuity. As long ago as 1875, Galton pointed 

 out that there is a sense in which the child 

 is as old as the parent; for when the parent's 

 body is developing from the fertilized ovum, 

 a residue of unaltered germinal material is 

 kept apart to form the reproductive cells, 

 one of which may become the starting- 

 point of a child. This idea has been in- 

 dependently expressed and more fully de- 

 veloped by Weismann, who states it thus: 

 "In development a part of the germ-plasm 

 [i.e. the essential germinal material] con- 

 tained in the parent egg-cell is not used up 

 in the construction of the body of the off- 

 spring, but is reserved unchanged for the 

 formation of the germ-cells of the following 

 generation." In many cases the future re- 

 productive cells are visibly set apart at a 

 very early stage before the division of labour 

 in body-making has more than begun; in 

 other cases where the future reproductive 

 cells are not visible till much later, we argue 

 by analogy that they are reproductive cells 

 because they have not shared in body- 

 making, but have kept intact the proto- 

 plasmic equipment — the full inheritance — 



