The interrelation of genetic and non genetic factors 
in development 
by Arend L. Hagedoorn, Ph. D. 
Verrieres le Buisson. 
The work of Mendel has placed. the study of development 
on a new and solid basis. From his work and that of his followers 
we have at last learned to distinguisli between the two kinds of 
factors in the development of the organisms^ so that we may 
now study them separately^ and find out what part each cathegory 
plays in ontogenetic development^ and in how far each can have 
furnished the material for a phylogenetic development of the 
difi^erent types. 
The object of this paper is to treat of the differences 
between the two sorts of factors in development, to point out 
their relation^ and the possibilities in Controlling this relation in 
some organisms for economic purposes. The lack of knowledge 
concerning the parts played by the genetic, transmitted factors 
on one band, ai^d the environment, the non-genetic factors on the 
other, in the development of the organisms, in pre-Mendelian times 
is very well illustrated by the Opposition of the views of Oscar 
H e r t w i g and W e i s m a n n on the subject. W e i s m a n n, building 
forth on Darwin's conception of evolution as caused by selection on 
small differences, individual Variation, has elaborated a vast 
complex of theories, concerning the Constitution of the „germplasm", 
numerous living, protoplasmic particles of difterent sorts, each 
mysteriously calling forth one special organ or tissue. Parting 
from the altogether justified consideration that the efiects 
of the environnient on the individual are not ti*ansmitted, he 
has tried to ascribe the whole ontogenetic development to 
transmittable, genetic causes, neglecting the direct importance of 
the environment for this development. Oscar Hertwig on the 
other band, realizing the enormous importance of all kinds of 
non-genetic factors for all the developmcntal })rocesscs, has gonc 
