THE FACTORS OF ORGANIC EVOLUTION. 109 
thousands of generations, and amid the most diverse 
circumstances, bears strong testimony to the great sta- 
bility of that living structure which is the basis of in- 
heritance. On the other hand, all experience goes to 
prove that the living substance of the body cells in gen- 
eral is readily modified, and that in a surprisingly short 
time. The fact of this great difference can not fail to 
be recognised ; its cause is at present merely a matter of 
conjecture. 
Weismann at one time supposed the cause of this to 
be an absolutely stable, absolutely separate, and per- 
petually continuous germ plasm. How- 
Germinal proto- ever, there is the most convincing and 
plasm relatively ahundant evidence that although the 
but not abso- s z 
lately stable, germ plasm is relatively very stable and 
continuous, it does not possess those 
divinely perfect characters ascribed to it. More re- 
cently Weismann has practically abandoned each and 
all of these characters,* and now, like a good Lamarck- 
ian, finds “the cause of hereditary variation in the 
direct effects of external influences on the biophores 
and determinants.” 
The outcome of the whole matter, then, is that we 
find ourselves much in the same position as we were be- 
fore Weismann denied the possibility of the inheritance 
of acquired characters. All hereditary variations are 
caused by the action of extrinstc forces on the germinal pro- 
toplasm, producing changes in its structure. Strangely 
enough, this proposition was admitted as a logical neces- 
sity by one who undertook by rigorous logic to prove 
the reverse. Since almost the only objection to this 
position was the one raised by Weismann, it may now 
be considered as definitely settled, and the only ques- 
* See Romanes’s Examination of Weismannism, 1893. 
