D.—ZOOLOGY. 83 
destructive anti-lens had been continually produced and had acted, its 
effect would have been cumulative. A constructive substance must, 
then, have also been continually produced to counteract it. Such a 
theory might perhaps be defended; but would it bring us any nearer to 
the solution of the problem? 
The real weakness of the theory is that it does not escape from 
the fundamental objections we have already put forward as fatal to 
Lamarckism. If an effect has been produced, either the supposed con- 
structive substance was present from the first, as an ordinary internal 
environmental condition necessary for the normal development of the 
character, or it must have been introduced from without by the appli- 
cation of a new stimulus. |The same objection does not apply to the 
destructive effect. No one doubts that if a factor could be destroyed by 
a hot needle or picked'out with fine forceps the effects of the operation 
would persist throughout subsequent generations. 
Nevertheless, these results are of the greatest interest and impor- 
tance, and, if corroborated, will mark an epoch in the study of heredity, 
being apparently the first successful attempt to deal experimentally 
with a particular factor or set of factors in the germ-plasm. 
There remains another question we must try to answer before we 
close, namely, “ What share has the mind taken in evolution?’ From 
the point of view of the biologist, describing and generalising on what 
he can observe, evolution may be represented as a series of metabolic 
_ changes in living matter moulded by the environment. It will natu- 
rally be objected that such a description of life and its manifestations as 
a physico-chemical mechanism takes no account of mind. Surely, it 
will be said, mind must have affected the course of evolution, and may 
indeed be considered as the most important factor in the process. 
Now, without in the least wishing to deny the importance of the mind, 
I would maintain that there is no justification for the belief that it 
has acted or could act as something guiding or interfering with the 
course of metabolism. This is not the place to enter into a philo- 
sophical discussion on the ultimate nature of our experience and its 
contents, nor would I be competent to do so; nevertheless, a scientific 
explanation of evolution cannot ignore the problem of mind if it is to 
satisfy the average man. 
Let me put the matter as briefly as possible at the risk of seeming 
somewhat dogmatic. It will be admitted that all the manifestations of 
living organisms depend, as mentioned above, on series of physico- 
chemical changes continuing without break, each step determining that 
which follows; also that the so-called general laws of physics and of 
chemistry hold good in living processes. Since, so far as living pro- 
cesses are known and understood, they can be fully explained in 
accordance with these laws, there is no need and no justification for 
calling in the help of any special vital force or other directive influence 
to account for them. Such crude vitalistic theories are now discredited, 
but tend to return in a more subtle form as the doctrine of the inter. 
action of body and mind, of the influence of the mind on the activities 
of the body. But, try as we may, we cannot conceive how a physical 
process can be interrupted or supplemented by non-physical agencies. 
