newly-hatched mound-bird, having struggled out of the degg-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.

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If instinctive behaviour implies the hereditary or t racially established neuro-muscular pre-arrangements for lea 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 t much of it. Educability and instinctive capacity are in inverse ratio. A chick usually degenerates into an overapti domesticated hen, but it is in its youth alertly intelligent dit 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 dropli 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.

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Reference may be made here to certain cases where an animal is misunderstood as 'unutterably stupid' because of its bewilderment when something has dis turbed 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

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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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on the two sides. An interesting fact is the not infrequent reversal of tropisms when a certain limit is crossed or when there is a notable change in the environment or in the animal's physiological condition. Some animals like scorpions and crayfish that are constitutionally light-shunning (negatively heliotropic) are unable to keep away from an unusually bright light. The little crustaceans called gammarids that are common in brooks are constitutionally light-shunning and given to hiding under stones; but if a few drops of acid be added to the water of the aquarium in which they are living, they become positively heliotropic! Some caterpillars are constitutionally wound-up to climb higher and higher on their food-plant (negatively geotropic), but when they reach full size and their physiological state changes, their forced movement' or tropism reverses, and they become as bent on going down as they previously were on climbing up. It is also the case that a tropism may be interrupted by another tropism or by individual initiative. The obligatory character of the tropism must not be exaggerated, but in the ordinary routine of the animal's life it is just the obligatoriness that makes them so profitable. In ninety-nine cases out of a hundred they work well, and even in subtle cases where rapidity counts for much, as when the male mosquito, automatically adjusting his antennæ and body, like & living gyroscope, is able quickly to find the female when she utters her shrill note, which is not to be confused with the buzzing common to both sexes.

The behaviour of the newly-hatched Loggerhead turtle, carefully studied by Howard and Parker, shows something a little different from ordinary tropisms. Suddenly ushered into a new world, the little creature hurries from its cradle in the sand to its future home in the sea. It is constitutionally bound to go down a slope rather than up (though it may climb if necessary), and it seems to be more influenced by blue than by other colours-two inborn preferences that may help it seawards-but careful experiment shows that its life-saving reaction is to move away from the more blocked and interrupted horizon and towards that which is open free. It is forced to go right.

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Allied, but again somewhat different, are racially

nregistered rhythms that have taken firm hold of the onstitution. The well-known green planarian worm, Donvoluta, abundant on the flat beach at Roscoff, comes but of the sand when the tide goes down, and disappears again at the first splash of the flow. When these tiny Worms are transferred to a tideless aquarium they exhibit the same rhythm as in the open, and continue appearing and disappearing with regularity for over a week. But we dare not use any psychological word like memory; what happens is due to a racial bodily enregistration. There is a hereditary rhythmic reactivity to periodic changes in the gravitational conditions, but the awakening of the reaction is probably helped by the changes in the amount of water and light. In a dark aquarium the rhythm disappears quickly. It is probable that racially established rhythms correlated with external periodicities play a part in animal behaviour greater than has been yet recognised, especially in regard to seasonal activities.

Thus gradually, on the inclined plane of animal behaviour, we reach the level of reflex actions, some simple and some complex, some detached and others bound together, but all depending on pre-established linkages between sensory neurons, adjustor or associative neurons, motor neurons, and the effector muscles. The earthworm jerks itself back into its burrow when the ground vibrates under the light tread of the blackbird's foot. The nestling opens its mouth at the touch of food in its mother's bill and then proceeds to swallow. Animal behaviour abounds in reflexes.

If it be granted that a germinal variation may express itself in structural improvements in the body, there is no particular difficulty in imagining the origin of reflex arcs and actions. When the rapidity and precision of the response is of survival value, the racial establishment of an improved reflex linkage is easy to understand. Yet the problem is perhaps unnecessarily obscured by excluding the operation of some degree of mental awareness which prompts the animal to put its inborn gifts to the test, especially when there any novelty in the circumstances. Instead of looking for mind' in the origin of the reflex, it may be shrewder to look for it in the testing of the hereditary equipment.

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