GENEOLOGICAL. 403 



body-cells has more than begun. In the development 

 of the threadworm of the horse, according to Boveri, 

 the very first cleavage divides the fertilised ovum 

 into two cells, one of which is the ancestor of all the 

 body-cells, and the other the ancestor of all the germ- 

 cells. In other cases, particularly among plants, 

 the segregation of germ -cells is not demonstrable un- 

 til a relatively late stage. Weismann, generalising 

 from cases where it seems to be visibly demonstrable, 

 maintains that in all cases the germinal material 

 which starts an offspring, owes its virtue to being 

 materially continuous with the germinal material 

 from which the parent or parents arose. But it is 

 not on a continuous lineage of recognisable germ- 

 cells, that Weismann insists, for this is often un- 

 recognisable, but on the continuity of the germ- 

 plasm — that is of a specific substance of definite 

 chemical and molecular structure which is the 

 bearer of the hereditary qualities. In develop- 

 ment a part of the germ-plasm, " contained in the 

 parent egg-shell is not used up in the construction of 

 the body of the offspring, but is reserved unchanged 

 for the formation 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. 



While early segregation of the germ-cells is in 

 many cases an observable fact — and doubtless the list 

 of such cases will be added to — the conceptisn of a 

 germ-plasm is hypothetical, just as the conception 

 of a specific living stuff or protoplasm is hypothetical. 

 We cannot demonstrate the germ-plasm, even if we 

 may assume that it has its physical basis in the stain- 

 able nuclear bodies or chromosomes. The theory has 



