LIFE 335 



On Darwin's hypothesis of pangenesis every cell of 

 the body throws off particles or gemmules which collect 

 in the reproductive cells. These gemmules, or " unde- 

 veloped atoms," are transmitted by the parent to the 

 offspring, they multiply by self-division, they may remain 

 undeveloped during early life, or even during several 

 generations, but when under the influence of suitable 

 environment they do develop, they become cells like those 

 from which they were derived. By aid of this hypothesis 

 Darwin was able to resume a great many of the facts of 

 heredity. Inheritance was simply the development of 

 the parental gemmules in the offspring ; variation could 

 be described partly by a commingling of the gemmules 

 of two parents, partly by a modification of the gemmules 

 of the parental cells due to their use or disuse.^ Now it 

 is quite clear that no biologist would have propounded 

 this hypothesis, but for the currency of corpuscular theories 

 in physics. Indeed, Weismann actually restates Darwin's 

 hypothesis in terms of molecules, and speaks of unknown 

 forces drawing these molecules to the reproductive cells 

 and marshalling them there." But as no physicist ever 

 caught an atom, so no biologist ever caught an " unde- 

 veloped atom," or gemmule. The validity of the concep- 

 tion can only be tested by the power it gives us of 

 resuming the facts of heredity, and it is no more disproved 

 by the statement that " gemmules have not been found in 

 the blood," than the atomic theory is disproved by the 

 fact that no atoms have been found in the air. If the 

 biologist has once grasped that the physicist is making a 

 metaphysical statement when he asserts the phenomenal 

 existence of corpuscles, then he will be the more ready 

 to admit that the non- finding of gemmules and the 

 " unknown forces necessary to control them " are not 

 arguments against a conceptual description of heredity, 

 but against a metaphysical projection of its concepts into 

 the phenomenal world. 



Weismann, who I think projects Darwin's gemmules 



^ Variatioji of Animals and Plants under Domestication, vol. ii. chap, xxviii. 

 '^ Essays on Heredity, pp. 75-8. 



