A reflex action of the

effort.* Were it not for this power which we have of withdrawing our attention, our intellect would be absorbed and wasted on the merest routine work, instead of being set free to appropriate and render practically instinctive, a continually wider and more important range of deliberate, purposive actions.

Attempts have also been made to explain "instinct individual. a form of "reflex action," or rather of that automatic response to felt stimuli called "sensori-motor action." † In a certain very wide sense of these terms that explanation may pass, but such is not the sense in which the term "reflex action," or "sensori-motor action," has (so far as we know) hitherto been used. The attempt to explain instinct by such actions, in the ordinary sense of those terms, is an attempt to explain a phenomenon by omitting its most striking characteristic. In reflex action and sensori-motor action, we have a sudden response to an unfelt or a felt stimulus, which response is more or less appropriate at the time of its occurrence, but has certainly no reference whatever to future events which are to occur long after the faintest waves of the stimulating action have died out. The very essence of instinct, however, is to provide for a more or less distant future, often, as we have seen, the future of another generation. It is essentially telic (ie. is directed to a definite end), and refers to circumstances future and unforeseen, at the time the instinctive action takes place. This explanation, then, is fundamentally and necessarily inadequate. It is like an explanation of the building of a house by "bricks, mortar, bricklayers, and hodmen," with the omission of all reference to any influence governing their motions, and directing them towards a common and predetermined end which is not theirs. But though we cannot explain "instinct" by these automatic responses to unfelt or felt stimuli, there is none the less a certain obvious affinity between them and instinct. In fact, all animal action is "reflex," in the widest sense of that term; for all such actions result, and are a reaction, from stimuli (internal or external) which are either felt or not felt. The effects of stimuli, moreover, differ according to what it is they stimulate. The ultimate * See above, p. 185. See above, p. 168.

protoplasmic particles of the innermost parenchyma of the body of man, and the naked isolated particles of protoplasm which compose the minutest and lowest organisms, react upon the stimulus of a certain degree of heat, of moisture, or chemical action. The various different tissues of which the bodies of organisms are composed severally react, upon stimulation, in different ways, the study of which constitutes. the science of the physiology of the tissues. The organs and systems of organs of the body have also their various modes of definite reaction, the consideration of which constitutes physiology as ordinarily understood. But this is not all. The entire body of a living creature reacts as one whole, in response to influences brought to bear upon it. This we see in the hibernation, or winter sleep, of bats and hedgehogs; in the effects of violent emotions of fear and anger, and in the results of sexual and reproductive influences upon the whole organism. The activities and reactions of the whole body of an animal-including the process of its individual development-form a separate department of the study of function, and may be called "the physiology of the individual."*

Now, inasmuch as function and structure vary together, and as the various actions of the organs of animals depend upon the various properties of the parts which act; so also the activities of each animal as a whole, its habits and instincts, are closely related to its structure. Were it possible for us to artificially construct an animal completely and then animate it, no doubt we should find we had endowed it with all the instincts pertaining to that particular kind of structure. They may, therefore, be said to be the sensori-motor actions of each animal as a whole, and may thus be explained as a form of reflex action in the highest and widest sense of that term. But the sense in which that term is used must be a very wide one, for instincts are not absolutely invariable. They are modifiable to a certain extent by circumstances, and by the powers of sensuous cognition an animal may possess. The absence of accustomed objects of sense, with the presence of others in their place, will (under the stimulus of hunger, or the felt

Or part of its pyschology, in the proper sense of that term (see below, chap. xxv., "Psychology and Physiology").

needs of the reproductive processes) lead birds in abnormal conditions to build their nests in unwonted ways. Similar abnormal influences will lead many creatures to seek their food (whether on land, in water, in the branches of trees, or beneath the surface of the earth) in modes other than those which up to that time have been adopted by creatures of their kind. Nevertheless, if we may call instinct "the reflex activity of a whole living organism,” that function remains one clearly distinct from all the other forms of vital activity which we have yet considered. Something, however, yet remains to be said about "instinct," considered as an outcome of the struggle for life which all organisms have to undergo. But that question cannot here be entered upon, because it must be preceded by some considerations concerning the relations which living creatures bear to their environment—their external relations — considerations to which the next

chapter will be devoted. The question must be relegated to the twenty-seventh, and last, chapter, which will treat of "evolution."

CHAPTER XXIV.

THE EXTERNAL RELATIONS OF ORGANISMS.

Groups of organisms differ greatly as to their relations to past time and their geographical distribution, while the life of individual organisms depends to a large extent upon other organisms living at the same time; and not only are individual organisms affected by their environment, but such affections may be inherited.

Relations to time and space-Inter-relations of organisms-Effects produced on organisms by their environment.

SOME of the external relations of organisms have been incidentally noticed in our last chapter. Without such notice, the functions of organisms could not have been considered; for respiration † and the formation of organic matter, take place through interactions between living organisms and their inorganic environment. The processes which are necessary to effect the nutrition of organisms § which feed upon other organisms, and the phenomena of parasitism, also involve external relations between living. creatures of different kinds. But these matters need now to be considered somewhat more at length. As the relations which exist between organisms and the inorganic world have been already sufficiently explained for the purpose of the present work, the other external relations of organisms may be treated of under three heads-(1) their relations to time; (2) to space; and (3) to one another.

* For an exhaustive notice of the influence upon organisms of their environment, together with a complete list of books and memoirs bearing on the subject, see a paper by J. Arthur Thomson, M.A., F.R.S.E., in the "Proceedings of the Royal Physical Society of Edinburgh," vol. ix., part 3, 1888. See above, p. 333. See above, p. 334.

See above, p. 161. § See above, p. 336.

Relations

to time

and space.

It is generally known that different kinds of animals and plants have successively inhabited the surface of this planet. The order of that succession has been far from regular; the past duration of different groups of organisms having varied greatly. Many kinds of animals have become extinct in certain regions in historic times, and some have become also absolutely and universally extinct. Thus wolves have disappeared from England since the time of Henry VIII, while only seventy years ago the great bustard wandered over the South Downs and Salisbury Plain. The dodo, the rhytina, the great auk, and the dinornis have, more or less recently, become absolutely extinct.

The only evidences we possess of past life, is afforded us by the five kinds of fossils before described.* This record is an exceedingly imperfect one; remains of animals and plants having been only here and there exceptionally preserved by some favouring accidents, and often in a very fragmentary manner. In most cases such remains seem to have been transported by water for greater or less distances, and buried in mud; and creatures which live habitually in or near water, form a very large proportion of those the hard parts of which have been thus preserved.

We have no space for even the briefest catalogue of the most generally interesting fossils. One or two, however, must be mentioned which bear upon problems of special interest treated of in this work.

The Laurentian rocks, in spite of their enormous thickness, have as yet afforded little evidence of life, and that only of very lowly organisms; but when even the lower Cambrian rocks were deposited, many Echinoderms and Brachiopods, Mollusks and Arthropods, were already in existence, while sharks and sturgeons are Devonian, and huge Batrachians, called Labyrinthodonts, characterize the coal measures. In the secondary epoch there existed a multitude of large reptiles, such as the marine Ichthyosauri and Plesiosauri, the terrestrial Dinosauria, and the ærial Pterosauria, which then flew as bats do now. The tertiary strata introduce us to the remains of creatures belonging

See above, pp. 313, 314.