12 THE TREND OF THE RACE 
cally collected facts. He postulated that the different organs of 
the body gave off into the blood, or other bodily fluids, minute 
living particles which he called gemmules, and which he supposed 
to be capable of growth and multiplication. The germ cells were 
supposed to have a special affinity for these gemmules, their 
function being to act as storehouses for these bodies. During 
development the gemmules were sorted out, each kind determin- 
ing the development of a part of the embryo into the kind of 
organ from which it was derived. 
This theory gave scientific expression to the traditional concep- 
tion of inheritance according to which the parts of the offspring 
are derived from corresponding parts of the bodies of their par- 
ents. It afforded also a means of explaining how characters 
acquired by the parents might be transferred to following genera- 
tions. Darwin, like most of his contemporaries, accepted the 
doctrine of the transmission of acquired characters which La- 
marck had postulated as the chief cause of organic evolution. He 
supposed that parts which are developed through exercise would 
produce more gemmules and that this would cause the corre- 
sponding part to be better developed in following generations. 
The hereditary effects of disuse were explained in a similar man- 
ner. Granting Darwin’s doctrine of pangenesis, the explana- 
tion of the transmission of acquired characters followed very 
naturally. But the fundamental difficulty of the doctrine lay 
in the artificial and improbable nature of its fundamental 
assumptions. Although ingeniously worked out and applied, 
the theory gained few followers, and as knowledge of the 
cellular basis of heredity came to be more minute and 
thorough, its incongruity with known facts became more and 
more apparent. 
Although the doctrine of pangenesis has now been given up, 
its influence upon subsequent theories of heredity is unmistakable. 
De Vries modified it by eliminating the hypothesis of the cen- 
tripetal flow of pangens, thus greatly simplifying it and avoiding 
some of its most improbable elements. The pangens were not 
supposed to be given off by the cells of the body and stored up in 
