48 



terminal buds. And the cells must contain this precious .substance with- 

 out showing its presence. Weismann says, " It is therefore clear that all 

 the cells of the embryo must for a long time function as somatic cells ; 

 and none of them can be reserved as germ-cells and nothing else." How 

 then does he explain the transferrence, through such long distances, of 

 the germ- plasm ? Keferring to the Hydroids he says : " I concluded that 

 the germ-plasm is present in a very finely divided and therefore invisible 

 state in certain somatic cells from the very be.iiinning of enibrj'^onic de- 

 velopment, and that it is transmitted through innumerable cell-genera- 

 tions to those remote individuals of the colony in which the sexual pro- 

 ducts are formed." 



But this transportation of the germ-plasm through so many generations 

 of cells is by no means the only difiiculty that besets Weismann's theory. 

 There is a number of plants, among them the begonia, which may be pro- 

 pagated from pieces of the leaves. It would almost appear as if single 

 cells of the leaf would reproduce the plant perfectly. Among the ferns 

 it is no uncommon thing for new plants to spring from the surface of the 

 leaves or of the stalks. Among mosses almost any cell of the root-hairs 

 will develop into new plants. As pointed out by Strassburger, the germ- 

 plasm must, in these cases, not merely travel through the plant to the 

 reproductive origans, but be widely diffused throughout every part of the 

 plant, and Weismann admits that this is the case. Similar phenomena 

 occur among animals. If the fresh water Hydra is divided into two pieces, 

 each will develop into a perfect Hydra. Trembly, in his experiments on 

 these things, minced some of them into as small pieces as he could, and 

 almost every piece developed into a perfect animal. It is stated that as 

 many as forty were thus reproduced from a single one. When certain 

 worms are cut in two, each part develops into a perfect individual. All 

 animals show some power of reproducing lost and injured parts. How 

 shall we explain these facts of reproduction and restoration? Is the 

 restoration of the hydra due to the presence of germ-plasm or not? If it 

 is claimed that it is due to the germ-plasm, it may be replied that it has 

 not reproduced the animal, but only a part, that part which was missing, 

 it may be the half of it or the greater part of it. When the worm is cut 

 in two one cut surface may develop a new tail, the other surface a new 

 head. Had the cut been made the thickness of a cell further forward, 

 those cells that in the first case engaged in developing a new head would 

 probably as readily have gone to work to produce a new tail. Does germ- 



