SCIENCE. 
231 
special form of the manifold language of sensation. And 
so of all the other organs of sense — they all perform their 
work in virtue of that purely mechanical adjustment which 
places them in a given relation to certain selected mani- 
festations of external force, and these they faithfully trans- 
mit, according to a code of signals, the nature of which is 
one of the primary mysteries of Life, but the truthfulness 
of which is at the same time one of the most certain of its 
facts. 
For it is upon this truthfulness — that is to say, upon a 
close and efficient correspondence between the impressions 
of sense and certain realities of external Nature — that the 
success of ever)' organism depends in the battle of life. 
And all Life involves a battle. It comes indeed to each 
animal without effort of its own, but it cannot be main- 
tained without individual exertion. That exertion may be 
of the simplest kind, nothing more than the rhythmic action 
of a muscle contracting and expanding so as to receive into 
a sac such substances as currents of water may bring along 
with them ; or it may be the more complex action required 
to make or induce the very currents, which are to bring the 
food ; or it may be the much more complex exertions re- 
quired in all active locomotion for the pursuit and capture 
of prey ; all these forms of exertion exist, and are all re- 
quired in endless variety in the animal world. And 
throughout the whole of this vast series the very life of 
every creature depends on the unity which exists between 
its sense-impressions and those realities of the external 
world which are specially related to them. There is therefore 
no conception of the mind which rests on a broader basis 
of experience than that which affirms this unity — a unity 
which constitutes and guarantees the various senses with 
their corresponding appetites, each in its own sphere of 
adapted relations to be exact and faithful interpreters of 
external truth. 
A still more wonderful and striking proof is obtained of 
the unity of Nature, and a still more instructive light is 
cast upon its source and character, when we observe how 
far-reaching these interpretations of sense are even in 
the very lowest creatures ; how they are true not only 
in the immediate impressions they convey, but true also 
as the index of truths which lie behind and beyond — 
of truths, that is to say, which are not expressly in- 
cluded — not directly represented — in either sensation or 
perception. This, indeed, is one main function and 
use, and one universal characteristic of all sense-impres- 
sions, that over and above the pleasure they give to sentient 
creatures, they lead and guide to acts required by natural 
laws which are not themselves objects of sensation at 
all, and which therefore the creatures conforming to them 
cannot possibly either see or comprehend. It is thus that 
the appetite of hunger and the sense of taste, which in some 
form or other, however low, is perhaps the most universal 
sensation of animal organisms, is true not only as a guide 
to the substances which do actually gratify the sense con- 
cerned, but true also in its unseen and unfelt relations with 
those demands or laws of force which render the assimila- 
tion of new material an indispensable necessity in the main- 
tenance of animal life. Throughout the whole kingdom of 
Nature this law prevails. Sense-perceptions are in all ani- 
mals indissolubly united with instantaneous impulses to 
action. This action is always directed to external things. 
It finds in these things the satisfaction of whatever desire 
is immediately concerned, and beyond this it ministers to 
ends of which the animal knows nothing, but which are of 
the highest importance both in its own economy and in the 
general economy of Nature. 
The wonderful instincts of the lower animals — the preci- 
sion and perfection of their work — are a glorious example 
of this far reaching adjustment between the perceptions of 
sense and the laws which prevail in the external world. 
Narrow as the sphere of those perceptions may be, yet 
within that sphere they are almost absolutely true. And 
although the sphere is indeed narrow as regards the very 
low and limited intelligence with which it is associated in 
the animals themselves, it is a sphere which beyond the 
scope of their intelligence can be seen to place them in un- 
conscious relation with endless vistas of co-ordinated ac- 
tion. The sentient actions of the lower animals involve 
not merely the rudimentary power of perceiving the differ- 
ences which distinguish things, but the much higher power 
of profiting by those relations between things which are the 
foundation of all voluntary agency, and which place in the 
possession of living creatures the power of attaining ends 
through the employment of appropriate means. The di- 
rect and intuitive perception of things which stand in the 
relation of means to ends, though it may be entirely disso- 
ciated from any conscious recognition of this relation in it- 
self — that is to say, the direct and intuitive perception of 
the necessity of doing one thing in order to attain to another 
thing — is in itself one of the very highest among the pread- 
justed harmonies of Nature. For it must be remembered 
that those relations between things which render them cap- 
able of being used as means to ends are relations which never 
can be direct objects of sensation, and therefore the power of 
acting upon them is an intuition of something which is 
out of sight. It is a kind of dim seeing of that which is 
invisible. And even if it be separated entirely in the lower 
animals — as it almost certainly is — from anything compar- 
able with our own prescient and reasoning powers, it does 
not the less involve in them a true and close relation 
between their instincts and the order of Nature with its 
laws. 
The spinning machinery which is provided in the body 
of a spider is not more accurately adjusted to the viscid 
secretion which is provided for it, than the instinct of the 
spider is adjusted both to the construction of its web and 
also to the selection of likely places for the capture of its 
prey. Those birds and insects whose young are hatched 
by the heat of fermentation have an intuitive impulse to 
select the proper materials, and to gather them for the pur- 
pose. All creatures, guided sometimes apparently by 
senses of which we know nothing, are under like impulses 
to provide effectually for the nourishing of their young. It 
is, moreover, most curious and instructive to observe that 
the extent of prevision which is involved in this process, 
and in the securing of the result, seems very often to be 
greater as we descend in the scale of Nature, and in pro- 
portion as the parents are dissociated from the actual feed- 
ing or personal care of their young. The Mammalia have 
nothing to provide except food for themselves, and have 
at first, and for a long time, no duty to perform beyond the 
discharge of a purely physical function. Milk is secreted 
in them by a purely unconscious process, and the young 
need no instruction in the art of sucking. Birds have 
much more to do— in the building of nests, in the choice 
of sites for these, and after incubation in the choice of food 
adapted to the period of growth. Insects much lower in 
the scale of organization, have to provide very often for a 
distant future, and for stages of development not only in 
the young but in the nidus which surrounds them. 
There is one group of insects, well-known to every ob- 
server — the common Gall-flies — which have the power of 
calling on the vegetable world to do for them the work of 
nest-building ; and in response to the means by which these 
insects are provided, the Oak or the Rose does actually 
lend its power of growth to provide a special nidus by 
which the plant protects the young insect as carefully as it 
protects its own seed. Bees, if we are to believe the evi- 
dence of observers, have an intuitive guidance in the selec- 
tion of food, which has the power of producing organic 
changes in the bodies of the young, and by the administra- 
tion of which, under what may be called artificial condi- 
tions, the sex of certain selected individuals can be deter- 
mined, so that they may become the mothers and queens of 
future hives. 
These are but a few examples of facts of which the whole 
animal world is full, presenting, as it does, one vast series 
of adjustments between bodily organs and corresponding 
instincts. But this adjustment would be useless unless it 
were part of another adjustment between the instincts and 
perceptions of animals and those facts and forces of sur- 
rounding Nature which are related to them, and to the whole 
cycle of things of which they form a part. In those in- 
stinctive actions of the lower animals which involve the 
most distant and the most complicated anticipations, it is 
clear that the prevision which is involved is a prevision 
which is not in the animals themselves. They appear to be 
guided by some simple appetite, by an odor or a taste, and 
they have obviously no more consciousness of the ends to 
be subserved, or of the mechanism by which they arc 
secured, than the suckling has of the processes of nutrition. 
