ON HEREDITY. 77 



that, at their next division, the molecules are separated to become 

 the somatic cells of the following generation. How can such a 

 process be conceivable, when the colony becomes more complex, 

 when the number of somatic cells becomes so large that they 

 surround the reproductive cells with many layers, and when at the 

 same time by an increasing division of labour a great number of 

 different tissues and cells are produced, all of which must originate 

 de novo from a single reproductive cell ? Each of these various 

 elements must, ex hypotke*i t give up certain molecules to the re- 

 productive 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 1 , 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. In short, we 

 become lost in unfounded hypotheses. 



It is well known that Darwin has attempted to explain the 

 phenomena of heredity by means of a hypothesis which corresponds 

 to a considerable extent with that just described. If we substitute 

 gemmules for molecules we have the fundamental idea of Darwin's 

 provisional hypothesis of pangenesis. Particles of an excessively 

 minute size are continually given off from all the cells of the body; 

 these particles collect in the reproductive cells, and hence any 

 change arising in the organism, at any time during its life, is repre- 

 sented in- the reproductive celj 2 . Darwin believed that he had by 

 this means rendered the transmission of acquired characters in- 

 telligible, a conception which he held to be necessary in order to 



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. 



2 See Darwin, 'The Variation of Animals and Plants under Domestication,' 1875, 

 vol. ii. chapter xsvii. pp. 349-399- 



