CHAP. XX 



Heredity 327 



" body " to form the reproductive elements of the offspring. 

 Thus he said, in a sense the child is as old as the parent, 

 for when the parent is developing from the ovum a residue 

 of that ovum is kept apart to form the germ-cells, one of 

 which may become a child. Besides Galton, Jaeger, and 

 Brooks, several other biologists suggested this fertile idea 

 of the organic continuity of generations. Thus it is ex- 

 pressed by Erasmus Darwin and by Owen, by Haeckel, 

 Rauber, and Nussbaum. But it is to Weismann that the 

 modern emphasis on the idea is chiefly due. 



Let us try to realise more vividly this doctrine of organic 

 continuity between generations. Let us begin with a fertil- 

 ised egg-cell, and suppose it to have qualities abcxyz. This 

 endowed egg- cell divides and redivides, and for a short 

 time each of the units in the ball of cells may be regarded 

 as still possessed of the original qualities abcxyz. But 

 division of labour, and rearrangement, infolding and out- 

 folding, soon begin, and most of the cells form the "body." 

 They lose their primitive characters and uniformity, they 

 become specialised, the qualities ab predominate in one 

 set, be in another, xy in another. But meantime certain 

 cells have kept apart from the specialisation which results 

 in the body. They have remained embryonic and un- 

 differentiated, retaining the many-sidedness of the original 

 egg-cell, preserving intact the qualities abcxyz. They form 

 the future reproductive cells — let us say the eggs. 



Now when these eggs are liberated, with the original 

 qualities abcxyz unchanged, having retained a continuous 

 protoplasmic tradition with the parent ovum, they are evi- 

 dently in almost the same position as that was. There- 

 fore they develop into the same kind of organism. Given 

 the same protoplasmic material, the same inherent quali- 

 ties, the same conditions of birth and growth, the results 

 must be the same. A single-celled animal with qualities 

 abcxyz divides into two ; each has presumably the qualities 

 of the original unit ; each grows rapidly into the form of 

 the full-grown cell. We have no difficulty in understanding 

 this. In the sexual reproduction of higher animals, the 

 case is complicated by the formation of the " body," but 



