4 The American Naturalist. [January, 
Thus reoriented in our work, it must. be observed that our 
remaining hypothesis also divides into alternative possibilities. 
Granting that the currents in the afferent nerves are diverse, 
still it remains possible either: That they may continue on, 
through the end-organ processes, each preserving its distin- 
guishing characteristic or phase of molecular activity till, at 
last, it articulates directly with its appropriate external stimu- 
lus. Or, that they may specifically terminate in the end-organs, 
and be linked, thence onward, to their outer stimuli by one — 
or more intermediate processes. These, if I am not mistaken, 
are the ultimate alternatives which remain for the solution of 
our problem. 
To decide whether, on the one hand, the afferent currents do 
preserve their specific nature through the end-organs, till they 
articulate with the external forces, or if, on the other, inter- 
mediate activities come between them and these last, is, there- 
fore, a crucial point in our investigations, and one of the impor- 
tant crux of our science. Unfortunately, however, it is one 
that the world’s present stock of knowlege is unable to deter- 
mine, and one that this paper must leave for future investiga- 
tion. The best authorities of our day present arguments on 
both sides, and too few facts of any kind are known to make 
any of them even approximately conclusive. Within the sphere 
of vision, the theories of Helmholtz, Herring, Ebbinghaus 
and Mrs. Franklin all demand intermediate retinal processes 
between the light vibrations and the neural conditions which 
must be conceived to be correspondent tothe final color-pictures. 
On the other hand it is the notion of Prof. Wundt that the vari- 
ous color-currents result immediately from diverse functions of — 
the light vibrations as they fall on the ends of the optic fibrils in — 
the retina; and Prof. Cattell and many others incline to follow 
this opinion. In the sphere of hearing it is well determined — 
that the sound-waves do not break immediately on the ends of ~ 
the auditory fibres; yet it is difficult even to guess whether the — 
final stimulus is a mediatory form of mechanical vibration, oF — 
is some unknown and perhaps chemical process set-up in the — 
end-cells in which the auditory fibrils terminate. Still less is — 
known regarding smell and taste, save that chemical processes, — 
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