as he does. One of the clearest instances of nonintelligent learning' is afforded by some experiments on earthworms which were confined in T-shaped tubes filled with soil, one path leading to a mild electric shock and the other to satisfaction. After 120-180 lessons, about six per day, the earthworms learned to avoid the electric path, making only one mistake or two out of twenty trials. But the lesson was learned not less thoroughly by headless earthworms!

On a different line of evolution from intelligent behaviour at its various levels are the diverse forms of instinctive behaviour, reaching its finest expression in ants, bees, and wasps. On its physiological side instinctive behaviour is a chain of reflex actions, the histological elements of which and their arrangement in sequences form part of the hereditary organisation of the animal. But in some cases it seems necessary to assume an active psychical correlate, and there is evidence that the instinctive chain of reflexes is suffused with an awareness that is more than sensitiveness to stimuli, and backed by an endeavour that is more than appetite.

For some spiders it has been shown that they construct their web true to the type of the species the very first time they try. Subsequent webs may be stronger and larger, but the first web has the characteristic architecture. As Rösch has shown, the worker honeybee serves an interesting apprenticeship within the hive, being promoted, so to speak, from task to task, all discharged instinctively, until after about a fortnight she passes into the new world of flowers and sunshine. But there the outstanding fact is that she enters and rifles difficult blossoms, collecting nectar as to the manner born. She fills her honey-sac, makes a bee-line for home, executes a peculiar nectar-dance (as Frisch has shown) on the honeycomb, makes her contribution to the communal wealth, and, after a short rest, flies off again for more. Although there are interesting idiosyncrasies, for it is a common saying among bee-keepers that 'bees never do anything always,' the behaviour is for the most part instinctive routine.

One of the most instructive illustrations of instinct is the behaviour of the Yucca moth which pollinates

the Yucca flower. Emerging from her cocoon, the female moth meets a mate in the air and flies from the encounter to visit a Yucca flower with ripe stamens. She collects a ball of pollen and carries it prominently beneath her mouth; she flies to another Yucca blossom and deposits some eggs in the seed-box; but on this visit she leaves the mass of pollen on the surface of the ripe stigma. The pollen-tubes grow down into the ovary; the egg-cells in the ovules are fertilised and begin to develop; the possible seeds become real seeds; and some of them form suitable food for the larvæ of the moth when these hatch out from the eggs. It is evident that there would be no seeds at all if it were not for the pollinating visits of the moth; it is evident that the nurture of the larvæ is ensured by the development of the seeds; and it should be noted that there are plenty of uninjured seeds left to ensure the propagation of the Yucca plant; but the important point for our present purpose is that an animal emerging into a new world goes through a performance hitherto untried, the success of which depends on a regular sequence of steps. An instinct is an inborn capacity for doing apparently clever things, without any need for 'learning' or apprenticeship, though this is not to be taken as denying that the instinctive performance is sometimes perfected by practice.

Many years ago, Sir Ray Lankester drew a clear distinction between (a) the little brain' type, reaching a climax in ants and bees, with a rich repertory of instincts and very little power of educability, and (b) the 'big brain' type, reaching a climax in the highest vertebrates, with relatively few instincts in the strict sense but with remarkable powers of learning or profiting by experience. From a different angle Bergson reached the same general conclusion, that instinctive and intelligent behaviour are on different lines of evolution, each with its own advantages and disadvantages. But these two great kinds of behaviour do not admit of very close comparison, still less of being pitted against each other.

It is useful to dwell for a little on the contrast between instinctive and intelligent behaviour. Instinctive behaviour requires no learning, but intelligent behaviour is based on what the naturally nimble brain learns. The

newly-hatched mound-bird, having struggled out of the egg-shell, has to continue to struggle out of the great heap of fermenting vegetable debris. If it stops to think or through fatigue, it perishes. If it continues its instinctive struggles it wins its way through, and hurries into the scrub. The Yucca moth, as we have seen, makes no tentatives; how different from the songthrush with its wood-snail!

Instinctive capacity is shared equally by all members of the species of the same sex, whereas intelligent capacity varies greatly from individual to individual. All female spiders of the same kind make an equally perfect web. Of course one must not make a dogma of this perfection of instinct, for mistakes are sometimes made when the consecutive manipulations are very intricate. Fabre tells us of the Calicurgus wasp that stings its captured spider near the mouth, thereby paralysing the poison-fangs; and then, safe from being bitten, drives its own poisoned weapon into a thin part of the spider's cuticle between the fourth pair of legs. But it is said that the precision of the thrust is not always perfect.

If an instinctive capacity implies on its physiological side the gradual elaboration of a number of neuromuscular linkages, activated by particular stimuli of vital importance, we can understand its characteristic limitation that it ceases to work well when there is some upsetting change in the circumstances. The full-grown Procession caterpillars crawl down the pine-tree on whose leaves they have been feeding, and march in Indian file over the ground, continuing until they find a soft place in which they can burrow and undergo their great change into moths. This persistent march or procession works well in most cases, but when Fabre adjusted the length of a file to the circumference of the stone curb of a fountain in his garden, and then brought the head of the first into contact with the tail of the last, they continued for a week crawling round and round in futile circumambulation-a striking instance of the limitations of instinct. A gleam of intelligence might have broken the spell, but, as Fabre said, 'Ils ne savent rien de rien.' A common form of the limitation is seen when part of the instinctive routine is forcibly

interrupted, for in many cases it cannot be resumed, and the animal passes to the next chapter, though that is quite inappropriate in the altered circumstances.

If instinctive behaviour implies the hereditary or racially established neuro-muscular pre-arrangements for a series of reflex actions, in which a serves in part to activate b, and b does the same for c, and so on, then the higher animals of the big-brained type do not show very much of it. Educability and instinctive capacity are in inverse ratio. A chick usually degenerates into an overdomesticated hen, but it is in its youth alertly intelligent and astonishingly quick to learn. With this is associated a paucity of instincts in the zoological sense. If hatched out in an incubator it does not recognise its mother's cluck when she is brought outside the door of the room; it does not recognise water as water, although it walks through a saucerful and will greedily swallow if a drop suspended from a finger-tip is brought into touch with its bill it will stuff its crop with unprofitable worms of red worsted! But these and a score of other significances are very rapidly learned.

Reference may be made here to certain cases where an animal is misunderstood as 'unutterably stupid because of its bewilderment when something has disturbed the ordinary instinetive routine. Prof. Whitman studied the varied behaviour of different kinds of pigeons when the eggs were removed during the brooding bird's brief absence and were placed a couple of inches or so outside the nest. Some kinds retrieved the eggs, some were satisfied with one egg, some made not the least effort to recover what had been removed, but sat patiently on nothing until the brooding instinct waned away. But it is a mistake to think a creature stupid when it fails to cope with the disturbance of a routine that is normally quite instinctive. The male rhea, or South American ostrich, is very assiduous in brooding, and makes it entirely his business, but before this part of the cycle begins, he has no interest whatever in an isolated egg that has been laid on his path. For obvious reasons there is not much parental care among fishes, yet it is sometimes exhibited in a high degree, as in sticklebacks and bubble-fishes, especially when the number of eggs is relatively small, and when there are

many chances of death in early life. For weeks the fish -usually the male-may guard the developing eggs, fasting all the time; and surprise has been expressed that this should sometimes end, in aquarium conditions at least, in the offspring falling victim to the parental appetite. Here again there is apt to be misunderstanding, for the instinct to seize a rapidly moving object, after being inhibited for a period by a strong parental instinct, not unnaturally reawakens when the cradle empties and the parental instinct dies away. In natural conditions there is usually a rapid scattering of the

progeny.

While the instinctive is an expression of non-intelligent racial enregistration, and does not necessarily require any 'learning' or understanding, one must not think of instinct and intelligence as separate entities or faculties. The whole life is a unity, and one must think of instinctive behaviour as possible without much mental correlate, whereas that is the true inwardness of all behaviour that is worthy of being called intelligent. What is inherited in the predominantly instinctive animals is a set of neuro-muscular predispositions of a very precise type, accompanied no doubt by a stream of feeling, as well as by a certain degree of awareness and the bent bow of endeavour. What is inherited in the predominantly intelligent animals is a highly-developed brain and the correlated mental aspect of imaging, experimentation, memory, and enjoyment.

If instinctive behaviour be regarded, on its physiological side, as a chain of hereditarily established reflex actions, there is a gradual transition to tropisms or obligatory movements, which play an important part in the life of lower animals. By a tropism is meant an inborn and automatically working adjustment of the body so that the two sides-or it may be the two eyes, the two ears, the two nostrils, the two antennæ, and so forth-are equally stimulated. The animal does not try to adjust itself; a tropism is an automatic means of securing physiological equilibrium. Thus the moth if it turns towards the light in flying past a candle is almost bound to fly into the flame. Thus the young eels or elvers must swim straight up-stream, for their bodies automatically adjust themselves to have equal pressure Vol. 249.-No. 493.

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