Appendix I. 175 



must originate de novo from a single reproductive cell," the 

 theory of pangenesis supposes the very contrary — viz., that 

 somatic changes in the past history of the phyla have not 

 thus originated in any reproductive cell. The idea of 

 somatic changes originating in reproductive cells belongs 

 to the theory of germ-plasjn ; but even this theory does 

 not suppose all the great number of different cells and 

 tissues which compose a complex organism to have ever 

 originated de novo from a single reproductive cell. 



The difficulty touching germ-cells becoming isolated, or 

 buried, by the phylogenetic increase of somatic cells, is 

 enforced in the immediately succeeding sentences, thus : — 



Each of these various elements [somatic cells] must, ex 

 hypothesis give up certain molecules to the reproductive cells ; 

 hence those which are in immediate contact with the latter 

 would obviously possess an advantage over those which are 

 more remote. If, then, any somatic cell must send the same 

 number of molecules to each reproductive cell x , we are compelled 

 to suspend all known physical and physiological conceptions, 

 and must make the entirely gratuitous assumption of an affinity 

 on the part of the molecules for the reproductive cells. Even if 

 we admit the existence of this affinity, its origin and means of 

 control remain perfectly unintelligible if we suppose that it has 

 arisen from differentiation of the complete colony. An unknown 

 controlling force must be added to this mysterious arrangement, 

 in order to marshal the molecules which enter the reproductive 

 cell in such a manner that their arrangement corresponds with 

 the order in which they must emerge as cells at a later period. 



Now I do not see much force in the suggestion that 

 those somatic cells which happen to be in immediate con- 

 tact with germ-cells, " must obviously possess an advantage 



1 " Or, more precisely, they must give up as many molecules as would 

 correspond to the number of the kind of cell in question found in the 

 mature organism." Of course by " molecules " Weismann means what 

 Darwin does by "gemmules." 



