in their physical development, is dependent, to a great degree at least, on some constitutional stimulus which is afforded by the changes which take place in the reproductive organs.

The existence of rudimentary organs and provisional larval stages is one of the most suggestive facts in the whole range of zoology, and the evidence that these things are a record of past history seems conclusive; although those who hold that their existence is accounted for by the discovery that they are a "recapitulation" add nothing, after all the centuries, to Aristotle's declaration that they are "for a token."

They who are most convinced that the historical significance of these structures is an adequate explanation of their presence, are also most emphatic in their repudiation of teleology, and in the rejection of the belief of Louis Agassiz, that they are part of the language in which the Creator tells us the history of creation; yet the assertion that their history accounts for their existence is as teleological as anything in Paley.

They who believe that inheritance is not the transmission of responsive actions, but the transmission of an adaptive mechanism, and that each change which enters into the history of development is a response to a stimulus, will have no difficulty in understanding that organs which were once adjusted to the external world may, after this adjustment has lost its meaning, be still retained, because they furnish physiological stimuli, which excite developmental changes in the organic mechanism.

If a physiological stimulus from the male reproductive organs excites the growth of weapons of defence, would the preservation of rudiments of these organs, by natural selection, for this useful purpose, be anything more than might be expected; even if some change in the method of reproduction should make their primary function useless?

Is there any evidence that any change which is due to nature, from the segmentation of the egg to old age, ever takes place without a stimulus, or are the actions which are due to nature beneficial, except so far as the environment is, on the average, like the ancestral environment? Since the gentle stimulation of the lips and tongue has been associated, in the past history of human infants, with the presence of milk which may be extracted

by sucking, the adjustment is beneficial; although the infant does not, as a matter of fact, obtain any milk at first, and although a finger or a rubber nipple on an empty bottle, or any other object of suitable size and texture, in the mouth of a hungry infant, excites the nerves and muscles so as to call forth the act of sucking, and, so far, to satisfy the calls of nature.

Preyer says "when I put into the mouth of the screaming child, whose head alone was as yet born, the ivory pencil or a finger, the child began to suck, opened its eyes, and seemed, to judge from its countenance, to be most agreeably affected. In the case of another child, which cried out immediately after its head emerged from the womb, I put my finger, three minutes later, into the child's mouth, and pressed it on the tongue. At once all crying ceased, a brisk sucking began, and the expression of the countenance, which had been hitherto discontented, became suddenly altered. The child, not yet fully born, seemed to experience something agreeable, and therewith during the sucking of the finger- the eyes were widely opened.'

Although changes which are directly due to nature do not take place without a stimulus, they do take place mechanically, or independently of experience, under the natural stimulus, or under any other which is applied in the same way. The blowfly, which is stimulated by the odor of putrid flesh to lay its eggs where the larvæ will find abundant food, sometimes lays them on the stinking arum, misled by its odor. In this case the deceptive stimulus resembles the normal one in certain sensible qualities, but it is most important, for reasons which will be given later, to note that the natural responses of living things may be called forth by any stimulus which is similar in its mode of application to the normal or natural stimulus, whether it is or is not similar in any sensible properties except those which act as the stimulus. The finger, which feels like a nipple, stimulates the infant and calls out the sucking response, but electrical stimulation of the lips and tongue, if applied with sufficient skill, might give the same result, although this does not resemble the nipple in any sensible qualities except the ones which effect the stimulation.

In the order of nature each stimulus is a sign with a significance, and our own reason, which consciously apprehends the

significance of natural signs, generally approves the responsive actions of living things, although we find that these living things are often misled by signs which we know to be illusions, which, while similar in some respects to those to which the organic mechanism is adjusted, signify something quite different from the normal or customary course of events.

As the nature of living things often leads to injurious or destructive actions, instinct is said to be blind or mechanical; for while no one can say whether the actions of the hermit-crab or those of the blow-fly, or those of the human infant, are voluntary or not, they are no more than the nature of these living things would lead one to expect, and this is as true when they are beneficial as it is when they mislead.

If the adjustments between living things and the external world were always beneficial, I do not see how the question whether or not their actions are voluntary could present itself; but the complexity of external nature is inexhaustible, and few natural adjustments are beneficial under all circumstances, for even a response to gravitation may mislead.

A growing plant needs the moisture and the soluble food which it may find under ground, in course of nature, by following the stimulus of gravity, and it also needs the sunlight and the air which, in the normal or natural order of things, are to be reached by upward growth. As the seed germinates, the radicle, stimulated by gravity, grows downwards, while the plumule, which does not differ essentially from the radicle in specific gravity, is impelled by its nature to grow upwards under the same stimulus; but each part grows by means of internal energy, and, while gravity is the stimulus which throws it into action, it is not the means by which the vital changes are brought about.

The response is beneficial, and the stimulus seems as trustworthy as anything in nature; yet the seeds often fall into places where it misleads, and if a germinating seed be placed on the edge of a horizontal wheel which turns slowly at a rate which makes the centrifugal force somewhat greater than the weight of the seed, the plumule grows towards and the radicle away from the centre, although no seeds which act thus can grow up to produce seeds in their turn. If plants think, a matter on which

I do not here express an opinion, they must know the order of nature to which they respond, and in that case the seed on the wheel would seem to be not only misled but deceived, exactly as a brood of chicks seems to us to be deceived by an imitation of the call of the mother hen; but the essential point is that, whether they know it or not, the changes in living things which are directly due to nature are beneficial only so far as the conditions of their life are, on the average, essentially like those in which the lives of their ancestors were passed.

Now the order of nature presents infinite diversity: the different ways in which events may be combined are innumerable; and no natural response can be judicious or beneficial under all circumstances. We accordingly find, in all the living things we know best, and are most intimately concerned with, a wonderful provision of their nature, by means of which those of their actions which are most apt to mislead are improved and perfected and developed by normal use, so that we are no longer able to tell what they will do from knowledge of their nature alone, since their actions are in part dependent on their training and experience, and on their individual contact with the world.

The question whether capacity for improvement through contact with the world is natural or not is much easier to ask than to answer. Are the benefits that attend training and education and experience part of the nature of living things, or do they add to nature something it did not before contain? Is knowledge of the world around us part of our nature, or does it add something new on to our nature? If it is natural, do we simply find or discover our nature, or do we make it or any part of it ourselves? Any answer we try to give is attended with difficulties. If living things make any part of their nature, the word must mean much more than is recognized in common usage; and yet the assertion that knowledge and experience and training add nothing to the nature of living beings is beset by difficulties which at first sight seem equally grave.

In some cases we can show that improvement by training is no more than might have been expected, for we can imitate it by means of stimuli which have nothing in common with the natural stimuli except the manner of their application. Normal

use strengthens muscles and increases their aptitude for doing their work, but as muscles may also be strengthened by massage, their improvement by use is no more than their nature might have led us to look for; nor do we find any more difficulty in attributing this beneficial response to nature than we find in the same explanation of the house-hunting actions of crabs.

All who have to do with animals admit that training can do no more for them than to make the best of their natural capacity, for they differ greatly in power to profit by experience; and the nature of each species sets impassable bounds to the power of individual animals to improve by practice. No one hesitates to attribute to deficient structure the inability of idiots to learn, and all admit that men of genius are born and not made, yet many hesitate to confess that their own more commonplace capacity for profiting by practice and growing wiser with experience is strictly limited by their nature, although this may be quite obvious to others. All know too well also that a dose of alcohol may make a man remember what never happened outside his own disordered brain, and perform responsive actions which, while criminal, might be prudent and commendable if the remembered experience were not a delusion; although the effects of contact with the world are usually far too complicated and diversified to be artificially imitated. As we are quite unable to tell with any minute accuracy what an animal with capacity for training will do under a stimulus, we must rely upon indirect evidence to show what the real significance of experience is.

If a chick is stung by the first honey-bee it catches, its future actions may be adjusted to the natural law that bees are dangerous; but if, before it is stung, it has captured and eaten stingless drones, it may act in accordance with the wider law that while bees are good for food some are dangerous. A careful observer, Mr. Gilman Drew, tells me that the chicks that are most destructive to bees pick out the drones, and he believes that these are the chicks which, before they were stung, learned to catch and eat bees, and that they have afterwards learned to let the stinging workers alone.

If slight differences in the mere order of events which are otherwise so much alike may lead to such differences in the con