6 The American Naturalist. [January, 
nervous system at different epochs, and finding serviceable 
articulation with environmental exigencies by means of the 
nerves and end-organs. If Lamarck is to guide us, then we 
must think of the various external forces as playing upon the 
surface of the developing organism, and modifying the nerve 
currents through to their central terminations in agreement 
with their own molecular, or molar characteristics and peculiar 
needs. The course of morphologic development would be oppo- 
posite in the two cases. In the first, the variations would begin 
in the nerve centers and make their way to the surface. In the 
second, the modifications would work from the surface, inward. 
Until a decision may be reached, therefore, between these two 
great morphologic principles, we shall be obliged, in estimat- 
ing the probable mode of origin of our senses, to keep up a 
double system of conjecture on this score, as well as on others. 
Its many difficulties having been set before us, we can now 
formally sum up, under its remaining contingencies, what may 
be called the residuary outlook of our general problem. We 
have remaining our two main postulates, that life began (O) 
with one sense or (M) with many ; our belief that the afferent 
nerve currents are diverse ; the alternatives that these currents 
articulate (d) directly, or (i) by intermediate end-organ pro- 
cesses ; and the two evolutionary principles, (w) the Weisman- 
nian and (l) the Lamarckian. With these before us, we have 
to cast up the possibilities of our mental origin under the 
combinations offered by their several limiting determinations. 
Beginning with the postulate, ‘O’ of one primary sense, and 
the doctrine ‘d’ of direct articulation, the course of morpho- 
logic history may be prospected as follows: 
(Od w). Under the Weismannian principle we may conceive 
that, from time to time, neural variations appeared, making 
possible certain molecular activities (sense-energies) whose res- 
pective peculiarities were diversely adapted to different envi- 
ronmental forces, and to physiological congruency and main- 
tenance within the creatures own organism ; and which varia- 
tions, therefore, were rejected or perpetuated according to the 
sum total of their fitness within the five spheres of evolutionary 
selection pointed out in our preliminary investigations. Look- 
il eas cm reel Seas CR A Ms ee oii ae, De Paar: SAE gee ete ito Sel BS. a tbe A 
