of other than mechanical behavior among animals to great lengths. Loeb introduces a paper written in 1890 on instinct and will in animals as follows:

"In the biological literature one still finds authors who treat the 'instinct' or the 'will' of animals as a circumstance which determines motions, so that the scientist who enters the region of animated nature encounters an entirely new category of causes, such as are said continually to produce before our eyes great effects, without it being possible for an engineer ever to make use of these causes in the physical world. 'Instinct' and' will' in animals, as causes which determine movements, stand upon the same plane as the supernatural powers of theologians, which are also said to determine motions, but upon which an engineer could not well rely.

"My investigations on the heliotropism of animals led me to analyze in a few cases the conditions which determine the apparently accidental direction of animal movements which, according to traditional notions, are called voluntary or instinctive. Wherever I have thus far investigated the cause of such 'voluntary' or 'instinctive' movements in animals, I have without exception discovered such circumstances at work as are known in inanimate nature as determinate movements. By the help of these causes it is possible to control the 'voluntary' movements of a living animal just as securely and unequivocally as the engineer has been able to control the movements in inanimate nature. What has been taken for the effect of 'will' or 'instinct' is in reality the effect of light, of gravity, of friction, of chemical forces, etc."

But Jennings, a very careful and industrious student of the behavior of the protozoa, whose studies have been perhaps more detailed and prolonged than those of any other investigator of the same subject, closes a fascinating volume on his work with the following paragraph:

"The present paper may be considered as the summing up of the general results of several years' work by the author on the behavior of the lowest organisms. This work has shown that in these creatures the behavior is not as a rule on the tropism plan-a set, forced method of reacting to each particular agent-but takes place in a much more flexible, less directly machinelike way, by the method of trial and error. This method involves many of the fundamental qualities

which we find in the behavior of higher animals, yet with the simplest possible basis in ways of action; a great portion of the behavior consisting often of but one or two definite movements, movements that are stereotyped in their relation to the environment. This method leads upward, offering at every point opportunity for development, and showing even in the unicellular organisms what must be considered the beginnings of intelligence and of many other qualities found in higher animals. Tropic action doubtless occurs, but the main basis of behavior is in these organisms the method of trial and error."

FIG. 265.-Diagram showing how the motile Protozoan, Stentor, reacts to light: A circular space half in light and half in dark; the animalcules collect in dark area; 1, 2, and 3 show the reaction of a specimen which came to the light line. (After Jennings.)

Different one-celled animals show differences in method or degree of response to external influences. Most protozoa will discard grains of sand, crystals of acid, or other indigestible objects. Such peculiarities of different forms of life. constitute the basis of instinct.

Instinct is automatic obedience to the demands of external conditions. As these conditions vary with each kind of animal, so must the demand vary, and from this arises the great variety actually seen in the instincts of different animals. As the demands of life become complex, so may the instincts become so. The greater the stress of environment, the more perfect the automatism, for impulses to safe action are necessarily adequate to the duty they have to perform. If the instinct were inadequate, the species would have become extinct. The fact that its individuals persist shows that they are provided with the instincts necessary to that end. Instinct differs from other allied forms of response to external conditions in being hereditary and continuous from generation to generation, and in being common to the species and not characteristic of the individual. This sufficiently distinguishes it from reason, but the line betveen instinct and reason and various forms of reflex action cannot be sharply drawn.

Some writers regard instincts as "inherited habit," while others, with apparent justice, doubt if mere habits or voluntary

actions repeated till they become a "second nature" ever leave a trace upon heredity. Such investigators regard instinct as the natural survival of those methods of automatic response which were most useful to the life of the animal, the individuals having less effective methods of reflex action having perished, leaving no posterity.

An example in point would be the homing instinct of the fur seal. When the arctic winter descends on its home in the Pribilof Islands in Bering Sea, these animals. take to the open ocean, many of them swimming southward as far as the Santa Barbara Islands in California, more than three thousand miles from home. While on the long swim they never go on shore; but in the spring they return to the northward, finding the little islands hidden in the arctic fogs, often landing on the very spot from

FIG. 266.-A "pointer" dog in the act of "pointing," a specialized instinct. (Permission of G. O. Shields, publisher of "Recreation.")

which they were driven by the ice six months before, and their arrival timed from year to year almost to the same day. The perfection of this homing instinct is vital to their life. If defective in any individual, he would be lost to the herd and would leave no descendants. Those who return become parents of the herd. As to the others the rough sea tells no tales. We know that of those that set forth a large percentage never come back. To those that return the homing instinct has proved adequate. This must be so long as the race exists. The failure of instinct would mean the extinction of the species.

The instincts of animals may be roughly classified as to their relation to the individual into egoistic and altruistic instincts.

Egoistic instincts are those which concern chiefly the individual animal itself. To this class belong the instincts of

feeding, those of self-defense and of strife, the instincts of play, the climatic instincts, and environmental instincts, those which direct the animal's mode of life.

Altruistic instincts are those which relate to parenthood

FIG. 267.-Part of branch of oak tree, showing acorns placed in holes in the bark by the California woodpecker, Melanerpes formicivorus bairdii. (From photograph taken at Stanford University, California.)

and those which are concerned with the mass of individuals of the same species. The latter may be called the social instincts. In the former class, with the instincts of parenthood, may be included the instincts of courtship, reproduction, home-making, nestbuilding, and care for the young.

The instincts of feeding are primitively simple, growing complex through complex conditions. The protozoan absorbs smaller creatures which contain

nutri

ment. The sea anemone closes its tentacles over its prey. The barnacle waves its feet to bring edible creatures within its mouth. The fish seizes its prey by direct motion. The higher vertebrates in general do the same, but the conditions of life modify this simple action to a very great degree.

In general, animals decide by reflex actions what is suitable food, and by the same processes they reject poisons or unsuitable substances. The dog rejects an apple, while the horse rejects a piece of meat. Either will turn away from the offered stone. Almost all animals reject poisons instantly. Those that fail in this regard in a state of nature die and leave no descendants. The wild vetches or "locoweeds" of the arid regions affect the nerve centers of animals and cause dizziness or death. The native ponies reject these

instinctively. This may be because all ponies which have not this reflex dislike have been destroyed. The imported horse has no such instinct and is poisoned. Very few animals will eat any poisonous object with which their instincts are familiar. unless it be concealed from smell and taste.

In some cases, very elaborate instincts arise in connection with feeding habits. In the case of the California woodpeckers (Melanerpes formicivorus bairdii) a large number together select a live-oak tree for their operations. They first bore its bark full of holes, each large enough to hold an acorn. Then into each hole an acorn is thrust (Figs. 267 and 268). Only one tree in several square miles may be selected, and when their work is finished all those interested go about their business elsewhere. At irregular intervals a dozen or so come back with much clamorous discussion to look at the tree. When the right time comes, they all return, open the acorns one by one, devouring apparently the substance of the nut, and probably also the grubs of beetles which have developed within. When the nuts. are ripe, again they return to the same tree and the same process is repeated. In the tree figured this has been noticed. each year since 1891.

The instinct of self-defense is even more varied in its manifestations. It may show itself either in the impulse to make war on an intruder or in an impulse to flee from its enemies. Among the flesh-eating mammals and birds fierceness of demeanor serves both for the securing of food and for protection against enemies. The stealthy movements of the lion, the skulking habits of the wolf, the sly selfishness of the fox, the blundering good-natured power of the bear, the greediness of the hyena, are all proverbial, and similar traits in the eagle, owl, hawk, and vulture are scarcely less matters of common observation.

Herbivorous animals, as a rule, make little direct resistance to their enemies, depending rather on swiftness of foot, or in some cases on simple insignificance. To the latter cause the abundance of mice and mouselike rodents may be attributed, for all are the prey of the carnivorous beasts and birds, and of snakes.

Even young animals of any species show great fear of their hereditary enemies. The nestlings in a nest of the American bittern when one week old showed no fear of man, but when