FOUNDATION OF A THEORY OF HEREDITY. 167 



If, according- to the received physiological and morphological 

 ideas of the day, it is impossible to imagine that gemmules pro- 

 duced by each cell of the organism are at all times to be found in 

 all parts of the body, and furthermore that these gemmules are col- 

 lected in the sexual cells, which are then able to again reproduce in 

 a certain order each separate cell of the organism, so that each 

 sexual cell is capable of developing into the likeness of the parent 

 body ; if all this is inconceivable, we must enquire for some other 

 way in which we can arrive at a foundation for the true under- 

 standing of heredity. My present task is not to deal with the 

 whole question of heredity, but only with the single although 

 fundamental question ' How is it that a single cell of the body 

 can contain within itself all the hereditary tendencies of the whole 

 organism ? ' I am here leaving out of account the further ques- 

 tion as to the forces and the mechanism by which these ten- 

 dencies are developed in the building-up of the organism. On 

 this account I abstain from considering at present the views of 

 Nageli, for as will be shown later on, they only slightly touch this 

 fundamental question, although they may certainly claim to be of 

 the highest importance with respect to the further question alluded 

 to above. 



Now if it is impossible for the germ-cell to be, as it were, 

 an extract of the whole body, and for all the cells of the organism 

 to despatch small particles to the germ-cells, from which the 

 latter derive their power of heredity; then there remain, as it 

 seems to me, only two other possible, physiologically conceivable, 

 theories as to the origin of germ-cells, manifesting such powers as 

 we know they possess. Either the substance of the parent germ- 

 cell is capable of undergoing a series of changes which, after the 

 building-up of a new individual, leads back again to identical germ- 

 cells ; or the germ-cells are not derived at all, as far as their 

 essential and characteristic substance is concerned, from the body of 



favourable opportunities afforded by such a medium, inasmuch as they are said to be 

 constantly circulating through the body ; so on the other hand we cannot understand 

 how the gemmules could contrive to avoid the circulation. Darwin has acted very 

 wisely in avoiding any explanation of the exact course in which his gemmules 

 circulate. He offered his hypothesis as a formal and not as a real explanation. 



Professor Meldola points out to me that Darwin did not admit that Galton's ex- 

 periments disproved pangenesis (' Nature/ April 27, 1871, p. 502), and Galton also 

 admitted this in the next number of 'Nature ' (May 4, 1871, p. 5). A. W. 1889. 



