1896.] The Biologie Origin of Mental Variety: 969 
plex and vastly variable, and assuming them to be so, the 
conclusion is inevitable that they should neither be produced 
or maintained with equal ease; and that, therefore, within 
the course of adaptation and survival their specific character- 
istics must have determined, respectively, their own advent 
and perpetuation. 
Third comes the vast region of fitness and selection, which 
must rise from the relative serviceableness of these several 
complex activities to The Environmental Forces, to whose stimu- 
lation they must join themselves for the creature’s welfare and 
preservation. That this sphere is likely to prove of central 
interest in our problem should be obvious, and because we are 
to give it much attention further on, we may limit ourselves 
to the bare statement of it here. 
A fourth region of evolutionary choice among possible 
sense energies must be found in the relative adaptiveness of 
their molecular complexities to the development and per- 
perfection of such peripheral or end-apparatus processes as are 
requisite or of profit for mediating between them and the en- 
vironmental forces. Within this field, more than anywhere 
else, perhaps, we are likely to discover the functions which 
most intimately determine the diverse forms of our perceptive 
organs, and that fix thereby the sorts of mental pictures de- 
pendent thereon. This, also, we are to discuss with some ful- 
ness presently. 
Finally, the factors in question must have oirmi 
bearings within our general physiology. These it will be nec- 
essary and important for Science in time to work out ; but they 
are of a nature so remote from psychologic problems proper 
that they need not be intruded further upon the limited space 
of this present paper. 
Their self-determinative fate within the realms of their 
Zoologic Genesis, their Physiologic Maintenance and Organi- 
zation, and their Environmental Adaptation, these, then, are 
what we have chiefly to study, in our present quest. And these 
lines being laid down, the following considerations pertinently 
thrust themselves forward, for our further guidance. It should 
be obvious at the outset that the nervous currents or impulses 
