FACTS OP INHERITANCE 133 



kept apart to form the reproductive cells, one of 

 which may become the starting-point of a child. 

 In many cases, scattered through the animal 

 kingdom, from worms to fishes, the beginning of the 

 lineage of germ-cells is demonstrable in very early 

 stages before the division of labour implied in 

 building up the body has more than begun. Let us 

 suppose that the fertilised ovum has certain 

 qualities, a, b, c, . . . x, y, z ; it divides and re- 

 divides, and a body is built up ; the cells of this 

 body exhibit division of labour and the structural 

 side of this, which we call differentiation ; they 

 lose their Ukeness to the ovum and to the first 

 results of the cleavage of the ovum. In some of 

 the body-cells the qualities a, h find predominant 

 expression ; in others the qualities y, z ; and so 

 on. But if, meanwhile, there be certain germ- 

 cells which do not differentiate, which retain the 

 quaUties a, 6, c, . . . x, y, z unaltered, these ■will 

 be iu a position by-and-by to develop into an 

 organism like that which bears them. Similar 

 material to start with, similar conditions in which 

 to develop — therefore, like tends to beget like. To 

 use Weismann's words : " In development a part 

 of the germ-plasm {i.e. the essential germinal 

 material) contained in the parent egg-cell is not 

 used up in the construction of the body of the 

 offspring, but is reserved unchanged for the forma- 

 tion of the germ-cells of the following generation." 

 Thus the parent is rather the trustee of the germ- 

 plasm than the producer of the child. In a new 

 sense, the child is a * chip of the old block.' " 



May we think for a moment of a baker who has 

 a very precious kind of leaven ; he uses part of this 

 in baking a large loaf ; but he so arranges matters. 



