REGULATORY PROCESSES IN ORGANISMS 219 
In the paper just referred to I have also attempted to show that 
at least a great variety of natural and experimental forms of 
reproduction, reduplication of parts, etc. are essentially processes 
of reconstitution following physiological isolation of parts. The 
chief difference between them and the cases of reconstitution 
following experimental section is, first, that the isolation of the 
part or parts is brought about within the organism physiologic ally 
and not by the crude method of cutting the organism into pieces; 
and second, that this isolation is usually partial at first and differs 
in degree and kind in different cases. 
And finally, I have called attention to certain evidence in sup- 
port of the view that the formation of sex cells and the develop- 
ment of organisms from them are processes not fundamentally 
different from other forms of reproduction, 7. e., that the sex cells 
are first physiologically parts of the organism like other organs, 
and that the development of a new organism from them is initiated 
by changes similar in character to those which occur in other parts 
capable of reconstitution, when they are physiologically or physi- 
cally isolated (Child, 710b, ’10c). 
The evidence bearing upon the first point is briefly as follows; 
first, the sex cells always arise in, or attain by migration particular 
regions of the body ina particular organism, therefore, their physio- 
logical correlation with other parts cannot be purely nutritive 
in character, for if it were, there is no reason why they should 
not take the most various positions in the same species. Second, 
they undergo characteristic differentiations during the life of the 
individual, as do other organs and these differentiations begin 
at a certain stage of development of the organism, 7. e., at or near 
the end of the period of vegetative growth. This cannot be ac- 
counted for by quantitative differences in nutrition at different 
stages, because the growth of the primitive germ cells in earlier 
stages often requires very large amounts of nutritive material. If 
this development is predetermined, then physiological correla- 
tion between the germ cells and other parts must have existed 
at some earlier stage, or else we are forced to a hypothesis of pre- 
established harmony, which amounts to some form of vitalism. 
Moreover, in organisms, which show both asexual and sexual 
