ORGA\IC EVOLUTION — THE FACTORS 59 



organism, when it is no longer directly affected by 

 those changes, to proliferate into an individual who 

 has the same kind of variation as the acquired variation 

 in the parent ? Why should not the result be enlarged 

 leg muscles or an enlarged brain or liver ? Is it con- 

 ceivable, if a man takes exercise in such a manner as 

 to enlarge the muscles of his legs, that the nutritive 

 fluids will thereby be so differently changed from what 

 they would be if he took such exercise as would enlarge 

 his arm muscles, as will confer on the germ such a 

 constitution as will cause it to proliferate into an 

 organism with enlarged leg muscles rather than 

 enlai'ged arm muscles? I think we may dismiss this 

 hypothesis also as unbelievable. 



The second of these theories is weighted with the 

 authority of a great and honoured name. Darwin, in 

 striving to account for the fact that complex and 

 heterogeneous multicellular organisms are able to 

 reproduce their like by means of germ cells, supposed 

 that each cell of the multicellular organism sends off 

 portions, which he called gemmules, of itself, which 

 gemmules, entering into the substance of the germ 

 cell, so affect its constitution as to cause it, when 

 fertilized, to proliferate into an organism like to that 

 from which it was derived. Since Darwin held that 

 acquired variations are transmissible, this, his theory 

 of " Pangenesis," must include the corollary that when 

 any part of the organism, for instance the arm muscles, 

 varies in such a manner as to increase the number of 

 its cells, the additional cells send off additional gem- 

 mules to each of the germ cells, whereas if it varies 

 in such a manner as to decrease the number of its cells, 

 a number of gemmules corresponding to the decrease 

 are in some way withdrawn from each of the germ cells. 



Now the germ cells of many animals, as for instance 

 of a man, are numbered by millions, the other cells, the 



