972 The American Naturalist. [December, 
certain to have been determining factors of the evolutionary 
relationship between our minds and bodies in any case, and 
by then passing on to observe that the sphere of this relation- 
ship would be vastly different respectively under our two rival 
theories regarding afferent nerve currents. Indeed, would be 
so different as to demand consequences, under one of these 
theories, so incompatible with existing facts that we shall be 
able to discard that theory altogether, thus reducing our diffi- 
culties, and giving us in the remaining theory an invaluable 
guide for our main investigation. 
This difference in evolutionary sphere comes to view the 
moment we recognize that under the Wundtian notion (of the 
sensory currents being different all the way through the nerves 
to the periphery and to the different environmental forces 
which respectively stimulate them) the forces determining the 
selection and perpetuation of these currents in the organism 
would include all the five regions in which we discovered it 
was possible for our “ molecular differences” (specific energies) 
to work with selective or evolutionary fitness—namely, the 
regions of Spontaneous Variation, of Nutrition, of Environ- 
mental Adaptiveness, of End-Organ Adaptiveness, and the 
vaguer sphere of our general physiology. On the other hand, 
and under the notion that the afferent currents are all alike, it 
should be plain that this likeness would cut off our central 
processes, regardless of their molecular differences, from all 
relative serviceableness either to the great world of environ- 
mental forces or to the intricate and indispensable mediating 
processes in the end-organs, and would thus reduce the sphere 
of their evolutionary reciprocity to the three remaining and 
apparently lesser fields. 
The significance of this is so great that we shall do well to 
set forth the connection between our senses and their stimuli, 
under this point of view, by an illustration. We may do this 
by imagining two wires coming to this desk, one of which 
is attached to a bell that is rung in accord with the velocity 
of the wind outside by an electric current, brought through a 
wire from a proper apparatus on the roof—a heavy wind ring- 
ing the bell violently, and a calm giving no ring at all—and 
