45 



tinct material. We may not be able to prove tbat it does not exist, but 

 we may do as we do with other ghosts, prove the superfluousness of its 

 existence. It is indeed a wonderful property that ia possessed by the 

 germ-cells of the animal, that of reproducing the form, organs, tissues, 

 and millions of cells of the parent : but the cells that can reproduce the 

 severed head of any animal, with its many sense organs, appear to me to 

 possess a property even more wonderful. For the germ-cell has a struc- 

 ture and corresi)onding capacities which are the ingrained results of 

 countless repetitions of the act of reproduction, while nothing of this 

 kind can be said with regard to the cells which reproduce the head, or 

 the tail, or the foot. It looks as if every cell o,f the whole body were 

 originally endowed with the capability of reproducing all the others in 

 <lue order; as if, indeed, something like Darwin's theory of pangenesis 

 were really true. Through subsequent high differentiation of structure, 

 or through unfavorable surroundings, the cells may not be able to accom- 

 plish the restoration, but they show that they possess at least a memory 

 of their old duties. 



In his last essay, that which treats of the ti'ansmission of acquired 

 characters, Weismann reasserts strongly their non-transmissibility, be 

 they produced in any way whatever. At the same time, he seems to me 

 to introduce a new explanation of variation, and to make admis^ons 

 which may prove fatal to his theory. It must be recollfcted that Weis- 

 mann has been contending for the stability of the germ- plasm; that, in 

 order to account for the variations that individuals show, he has invoked 

 the agency of sexual mixture, which he regards as an invention of nature 

 for that special purpose; that he has claimed that animals reproducing 

 by parthenogenesis can undergo no adaptive changes. When speaking 

 of the effect of external influences he says : " Without altogether denj^- 

 ing that such influences may di'cctly modify the germ-cells, I neverthe- 

 less believe that they have no share in the production of hereditary indi- 

 vidual differences." He has just previously maintained that the trans- 

 formation of a species can take place only through the accumulation of 

 these individual differences. Now in the last essay, in discussing certain 

 objections which have been urged against his doctrines, he contends that 

 external conditions, light, heat, moisture, nutrition, and their opposites, 

 can produce great changes in the body, but none directly in the germ- 

 plasm. He grants, however, that the environment may act indmctly on 

 the germ-plasm, so as to bring about important changes in the characters 



