IV.] FOUNDATION OF A THEORY OF HEREDITY. 1 69 



parts of the body of both sexes during copulation, and is ani- 

 mated by a bodily force ; according to this theory also, the 

 sperm from each part of the body reproduces the same part\ 



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 collected 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 like- 

 ness of the parent body ; if all this is inconceivable, we must 

 enquire for some other way in which we can arrive at a founda- 

 tion for the true understanding 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 here- 

 ditary tendencies of the whole organism ? ' I am here leaving 

 out of account the further question as to the forces and the 

 mechanism by which these tendencies 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 import- 

 ance 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 



^ Galton's experiments on transfusion in Rabbits have in the mean 

 time really proved that Darwin's gemmules do not exist. Roth indeed 

 states that Darwin has never maintained that his gemmules make use of 

 the circulation as a medium, but while on the one hand it cannot be 

 shown why they should fail to take the 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 experiments 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. 



