810 THEORY OF EVOLUTION. 
was already definitely predisposed, and to which the 
environmental change supplied only the stimulus. (2) We 
have not at present sufficient data to enable us to state that 
changes arising in or acquired by the Jody of an individual 
organism as the result of surrounding change do as such 
in any degree specifically affect the reproductive cells. In 
other words, we cannot at present say that “ environmental 
modifications” are transmissible. And if they are not, 
their importance in evolution is only indirect. 
(4) Changes due to Function (= Functional Modifications) 
It is an undoubted fact that the bodily structure of an 
animal may be changed by the increased use of certain 
parts, or the disuse of others,—in short, by some change of 
function, which may be directly prompted by some change 
in the external conditions of life. But important as these 
functional changes and their results are to the ¢vdividual, 
we are uncertain as to their importance for the race, for 
we do not know to what extent (if any) the results are 
transmissible. 
(c) Variations due to Changes in the Germ Cells 
In many cases of variation, particularly those which 
appear in early life, it is not possible to suggest any 
environmental or functional condition which may be 
regarded as the stimulus or the cause. We are led in 
such cases to believe that the variation in bodily structure 
or habit is the expression of some novelty in the proto- 
plasmic constitution of the germ cells. Then, hiding our 
ignorance, we say that the variation is germinal, con- 
stitutional, congenital, or blastogenic. It seems to lead 
to clearness if we call these germinal changes and their 
results variations, keeping the term modifications for those 
changes [(2) and (4)] wrought upon the body as the result 
of environmental or functional influences. 
But why should there be changes in the germ cells? 
Perhaps because living matter is very complex and un- 
stable, and because it is of its very nature to differentiate 
and integrate and grow; perhaps because the immediate 
environment of the germ cells (blood, body cavity fluid, 
sea-water, etc.) is complex and variable. Moreover, every 
