110 FOOT-NOTES TO EVOLUTION. 
tion before us, then, is: How can extrinsic causes 
modify the structure of the germinal protoplasm ? 
Since by his own admissions, as Romanes has shown, 
the most characteristic features of Weismann’s system, 
both as to inheritance and evolution, have been virtually 
abandoned, it seems to some that his theories have been 
of no real value, and that, like an zgnis fatuus, they have 
only served to lead biologists astray far from the path 
of science into the dangerous quagmires of speculation. 
I do not share any such opinion. Apart from his splen- 
did observations and the great stimulus to investigation 
which Weismann’s theories have furnished, there remain 
many elements of permanent value in his work. 
Osborn * thinks that Weismann’s most “permanent 
service to biology is his demand for direct evidence of 
the Lamarckian principle.” It seems to me that his 
greatest service consists in the emphasis which he has 
laid upon the intrinsic factors of development and evo- 
lution as opposed to the extrinsic factors, a thing which 
he has indeed overemphasized but which has sadly 
needed a strong defender in these later years. Largely 
as an outcome of his work we now recognise the possi- 
bilities and the limitations of the selection theory as 
never before, and we also recognise that many of the 
evidences which were adduced in support of the La- 
marckian factors are not conclusive, while the method 
of securing conclusive evidence is clearly marked out. 
Whatever we may think of his theories, this certainly is 
no slight service. 
5. It is by no means an easy task to determine 
whether the influence of extrinsic forces has really 
reached the germinal protoplasm and modified its struc- 
ture; much more difficult is it to determine how that 
* Osborn. The Unknown Factors of Evolution. Biological 
Lectures, 1894. 
