772 THEOR Y OF E VOL UTION. 



environmental influence, and those to which the organism 

 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 body 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. 



(b) 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. This change of or in function may be directly 

 prompted by some change in the external conditions of life, 

 or it may be the expression of a deeper variation in the 

 animal's material constitution or mental character. But 

 important as these functional changes and their results are 

 to the individual, 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 t/ie 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 ex- 

 pression of some novelty in the protoplasmic constitution 

 of the germ cells. Then, hiding our ignorance, we say that 

 the variation is germinal, constitutional, congenital, or blasto- 

 genic. It seems to lead to clearness if we call these germinal 

 changes and their results variations, keeping the term 

 modifications for those changes [(a) and (l>)] 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 unstable, 

 and because it is of its very nature to differentiate and 

 integrate; perhaps because the immediate environment of 



