stated that a monkey that had learned to screw and unscrew a handle from a broom had learned "the principle of the screw." This is entirely erroneous. The monkey merely observed that a certain movement given to the handle caused it to separate from the broom, and inferred perceptually that the same result would always follow from the same action.

It is evident that a sound comparative psychology of the animal kingdom, or even of a few of the highest species, is beyond the present possibilities of science.

CHAPTER X

INSTINCT

1. General Usage of the Term-2. Careful Usage of the Term— 3. Examples of Instinct-4. The Origin of Instinct

IN considering the mental life of animals, we must settle how far it is comparable to that of man. We judge of the mental processes of human beings, other than ourselves, from their actions; and we can only do the same when dealing with animals. If we often err in inferring the mental states of our fellow-men, how much more are we liable to error when we are considering creatures different from ourselves. Still, believing as we do in the continuity of life, both objective and subjective, by careful proceeding it is probable that in time we may arrive at a certain state of precision and exactness in comparative psychology.

Since the idea that is formed of the world is gained entirely from sensations, the world of every creature must be largely constructed from its dominant sense; in a dog, for instance, from scent.

In common speech the actions of animals are all ascribed to instinct. The notion which underlies the term is, that while the actions of men are determined by reason, those of animals are prompted by a blind power of doing that which is fitted to the successful conduct of their lives. This, as we shall see, is a notion that requires modification.

1. General Usage of the term Instinct.-Every one has a general notion of what is meant by instinct, but few are

agreed as to the precise usage of the word; thus when the birds build their nests, or when the bees collect honey and form their combs, their acts are with one accord said to be instinctive; but some would demur at using such a term to describe the love of parents for their children, the courage of brave men, or the artist's perception of beauty. But, even supposing we agree to mean by instinct all those actions which are neither simply reflex nor purely rational, there will still remain great difference of opinion as to its origin. Thus the love of parents will not be imagined as due to practice, either in the individual or its ancestors, but rather to take origin in some hidden necessity of nature; while the rapid closure of the eyes as protection from an expected blow would seem in all likelihood to have begun in a rapid exercise of intelligence, which, by being often repeated, had ceased to be accompanied by conscious effort.

It seems to us that there is still need of a vast amount of observation and experiment before a theory of the origin of instinct that will be at all satisfactory can be framed. As already remarked, it is not easy to decide even in what sense the term ought to be used. This being so, we shall content ourselves with mapping the field of thought and indicating the lines of inquiry that must be followed before a just view of the subject will be possible.

If we arrange examples of all the movements of animals in the order in which they are performed in the lifetime of the individuals, not limiting ourselves to those acts which involve the whole organism, but considering also those which a single organ or mass of tissue may execute, we shall see at a glance all the possible varieties of activity with which we can be concerned. It is, of course, only the movements of comparatively large masses of tissue with which we can deal at present. The molecular movements which lie at the base of all the visible ones are as yet almost unknown.

Even before birth, visible movements of the parts of the higher animals occur; as, for instance, the beating of the heart. Such movements may be either "automatic" or At birth, in addition to such movements of its parts,

reflex.

the organism acts as a whole; it reacts to its environment, and in time performs "voluntary " actions.

The acts of the parts of an organism may be—

(1) "Automatic," as, for example, the beating of the

heart.

(2) Reflex, as, for example, the intestinal movements which force the food through the alimentary canal, or the movements involved in sneezing. (3) Mixed actions which are partly automatic and partly reflex, such as the respiratory movements. The movements of the entire organism may be of a very complex nature. They may be

(1) Reflex; as when we start at a sudden noise.
(2) "Innate," commonly called instinctive; these are
best observed in newly-born animals, for in them
intelligence, which must be based upon experience,
is necessarily at a minimum.

(3) "Habitual," such as are rapidly learned and are
then performed without mental effort, which imply
an innate capacity, and are therefore allied to (2).
(4) Intelligent, such as imply mental activity, which
consists in the combining and rearranging all the
other possible acts of the order—(1), (2), or (3);
and which may be recognised in all adaptations
to novel circumstances.

This classification possesses most obvious faults, but it has certain advantages. It reveals some of the difficulties that delay the would-be definer of instinct. For the essential criterion of an instinctive action is that all the machinery for its performance, as a reflex to a certain stimulus, lies ready formed within the organism; but the apparently insoluble questions present themselves, How soon may not actions be modified by intelligence? and How in a mature animal with considerable experience is one to separate the purely instinctive acts from the intelligently modified instinctive acts?

Also it is evident that "habitual" actions may be "instinctive" actions deferred until the creature be further developed, as the flight of many birds is deferred; or they may

be actions in the formation of which intelligence has had a considerable share.

Now all these activities of an entire organism may be studied from four points of view :

(1) Of natural history, or general description, such as
occurs here and there throughout this work:
(2) Of physiology, or the analysis of the muscular,
nervous, and other mechanisms involved; as
treated generally in the last chapter:

(3) Of psychology, or the investigation into the states
of consciousness and mental processes concerned ;
as sketched in the last chapter:

(4) Of ætiology, or study of the factors in their origin

and development.

We shall first define more carefully than we have yet done what we shall speak of as instinct, then give a few examples, and finally discuss the aetiology of it.

2. The Careful Usage of the term Instinct.We have enumerated all the possible varieties of action, and the possible states of consciousness with which they may be associated have been described in the last chapter. If we retain the use of the term instinct we must explain to what order of activity we shall apply it. In our use of the term we shall not strive after any great precision; for, as already noted, the difficulty of precision seems to us to be at present insurmountable. In a general way we shall call any action which does not require for its execution any immediate exertion of perceptual inference an instinctive action. Thus a burned child dreads the fire; such dread and its consequent avoidance of fires may, with propriety, be termed instinctive. After the first burn the avoidance will, for a short time, be the result of perceptual inference; but in perhaps a few days only the avoidance becomes "instinctive"; or it might be called "habitual," as hinted previously. It is, of course, to be understood that an "instinctive " action is not necessarily the result of this "lapsed intelligence," as it has been called. Thus, when a worm wriggles away from a fire it probably has not at any time reasoned out to itself the advantages of such procedure,