254 JOURNAL OF COMPARATIVE NEUROLOGY. 
psychical alongside of what we call physical energy. For, ac- 
cording to all scientific principles, it is quite superfluous; it 
accomplishes nothing that can be measured by scientific appa- 
ratus; it is inert and useless. It isa mere phantom which a 
persistent metaphysical superstition conjures up to mock at the 
supposed materialism of science. Yet even Huxtey retains a 
sorry place for the psychical in this sense as a sort of epi-phe- 
nomenon, like the bell on a clock or the whistle on a steam- 
boat. Whatever truth the theory of psycho-physical parallel- 
ism may contain, it cannot lie in the conception of an onto- 
logical dualism of mind and matter. 
What, then, is the true relation of the psychical and the 
physical? Itis this. The psychical and the physical are re- 
lated as function and structure are related in biology. The 
biologist does not hypostasize function and make a separate 
form of energy out of it, which then is supposed to act causally 
upon structure. Some biologists ave attempted to conceive 
of the function as in some sense preceding the organ, of func- 
tion as preceding structure. But this notion has been called, 
what it certainly must remain when stated in this form, the 
biological paradox. Its paradoxical nature really arises from a 
false statement of the problem. It is as false to conceive of 
function as preceding structure as it is to conceive of structure 
as preceding function. A truer statement would be that the 
function is the meaning or significance of the structure. By 
the function of an organ is meant its characteristic activity or 
behaviour. The function of an organ is the meaning of that 
organ as expressed in its activity. All genetic classifications in 
science are classifications based on differences of function. It 
I want to understand the meaning of any structure I ask how 
it functions. Function in biology is another word for meaning 
or significance. 
It is in this way that the psychical is related to the phys- 
ical. Matter, so to speak, is the structure, of which mind is the 
function, and the meaning or significance of matter comes out 
only in its activity, only as it functions. The psychical is not 
another form of energy existing alongside of or in addition to 
