Passing now to the smaller trenches of the front line I have chosen as the first of them a small study of the varieties of epidermis found in mammals. With the exception of aquatic mammals so few of this, the greatest vertebrate class, are not clothed with hair that it is only on the comparatively hairless body of man, with its third of a million fine hairs, that the varieties of epidermis can be broadly studied. Much of this chapter will resolve itself into a considera­tion of the palmar and plantar surfaces of certain mammals, where no hairy covering obscures the operation of stimulus and response.

I assume that the foregoing phenomena of hair-direction have chosen and raised on his shield their own king. But here I must ask of the succeeding groups when they say, “I am, Sir, under the King, in some authority,” the question, “Under which King, Bezonian, speak or die”—

Shall it be Darwin’s Personal Selection?
Roux’s Cellular or Histonal Selection?
Wallace’s and Romanes’ Sexual Selection?
Weismann’s Germinal Selection?
The rule of Mendel?
Selection of mutations according to de Vries?
Or shall it be the barbarian king Plasto-diethesis?

Which indeed of the seven kings will they choose, if I may thus personify them? I may, perhaps, urge on them the mild and tolerant rule of Lamarck and Darwin rather than that of the other anointed sovereigns, hoping this cannot be taken as an attempt to influence the jury through the Press in a case which is still sub judice.

Stimuli and Response.

The skin over the trunk and limbs of man is exposed to stimuli of pressure, friction, heat, cold and wind in very different degrees, according to the part which it covers. I do not here refer to nocuous, or so-called noci-cipient stimuli, as being too casual in their incidence for the question in hand. Broadly the ventral surface of the neck and trunk differ much, in respect of the qualities of their epidermis, from the dorsal. The skin over the former is softer, thinner and more flexible than the latter, which is in adult life thick, hard and with larger openings of the sebaceous glands. As the two main layers of the skin are so closely united it is impossible to state any general rule as to the parts played in this manufacture by the epidermis and dermis respectively. Altogether the skin from the dorsal surfaces of mammals provides a much denser fabric than the latter, and different qualities of leather are obtained from different regions. Corresponding differences of texture are found on the extensor and flexor surfaces of the limbs, especially on the hands and feet. In the course of his long evolution from a hairy stock, whether simian as we thought yesterday, or a lower one as Professor Woods Jones suggests to-day, these dorsal surfaces of neck, trunk and extensor surfaces of limbs have been exposed through countless generations of men to vastly more stimuli of friction, pressure, and response, than those of the ventral and flexor regions. As man’s hairy covering diminished, through some mysterious and at present unrecognised cause, these stimuli became increasingly potent in producing a tissue denser than that of the more protected ventral parts where all forms of these stimuli are slight. I do not claim that this was a phenomenon that began with man, for in a measure it was present in those forms which preceded him, and in many related mammals under the cover of their hairy covering.

When we remember, or conceive what a large portion of each of his 24-hours even in his earliest form throughout life man must have spent, as he still does, in lying on his back or sides, and in sitting with his back against a supporting object, and with his gluteal and ischial regions pressed hard against whatever seat he has selected in cave or drawing-room, we need not travel far in thought to understand how great has been the preponderance of stimuli from friction and pressure on the dorsal and extensor surfaces over those on the ventral and flexor—and here comes in our familiar “total experience” with stimulus and response spread over a vast stretch of time. It must be borne in mind that from the facts of the case a very large number of individual men and women were exposed to similar, but not the same stimuli at each stage of the process involved. It is matter of common knowledge that not only on the palm and sole of man, but on regions where the skin is not specialised in that remarkable manner that is found in those regions, but also in others, that increased pressure and friction will very soon cause a harder and thicker growth of epidermis, as on the skin over a projecting bone in club-foot, over the shoulder where a weight is constantly carried, on the knuckles of many manual workers, and over the patellÆ of a devout Roman Catholic, as I have often seen.

On the other hand what conditions more calculated to thin and soften the skin could exist than those operating on the ventral and flexor surfaces, axillÆ, groins, external genitals and the bends of the elbow and knee-joints, where pressure, with little friction and greater warmth and moisture prevails? I need do no more than ask which is the more reasonable of the two forthcoming explanations of such phenomena, on the one hand that they are adapted for, and on the other adapted by this experience? I doubt if at any stage of the long process this slow manufacture of differing fabrics ever conferred on man any survival value or better matrimonial prospects. At any period or stage which I have supposed it can only be claimed for the results on the skin that they did not cause the animal to pass through the meshes of the sieve, and theoretically might be classed among the indifferent modifications, even if they added a little to the comfort of their possessor.

Skin of Palm and Sole.

One can examine in more detail the remarkable form of skin which is found to cover the palmar and plantar surfaces in many mammals. It is highly specialised and appears in many degrees of efficiency for the purposes, or uses, of walking and climbing, grasping and discrimina­tion of objects. With two or three insignificant exceptions these are the only regions even of man’s body where hairs do not grow in the normal state, and in most other mammals hair is absent from the component parts or pads, which correspond to our palms and soles. In the absence of hairs and sebaceous glands and the presence of as many as 320 sweat-glands to the square centimetre, and especially the papillary ridges, the mammalian hand and foot present a fruitful field for study. They have been studied by none more earnestly and thoroughly than Dr. H. Wilder Harris and Mrs. Wilder Harris (nÉe Inez Whipple). This small area of skin as an organ for grasping and discrimina­tion has been studied by persons from different, but not conflicting points of view. Time would fail me even to mention these, but I would recall here one aspect of the matter, that is the name given to it by these eminent authorities, Friction Skin. I think I do them no injustice, nay even honour, when I claim them as allies for us “Old Contemptibles” in the struggle, Lamarck v. Darwin in respect of these characters of the “mammalian chiridium.” This is a term employed by them for the hand and foot of all mammals, and is very convenient for descriptive purposes. From this point of view this organ has been produced from more generalised ancestral structures by reason of friction and pressure, and not for the purpose of resisting them, at least in their initial stages—again, adapted by and not adapted for meeting those forces. There are other views of the matter held by Pan-Selectionists, notably that of Dr. Hepburn, in regard to the papillary ridges. He would, as I gather, treat them as primarily induced, by selection, for the better grasping of objects cylindrical or more or less globular. I have referred elsewhere63 at some length to this in a book describing the examina­tion of the hands and feet of eighty-six species of mammals. The varieties of epidermis were divided into the smooth, corrugated, scaly, nodular, hairy, rod-like and ridge-covered forms, also four mixed varieties, such as corrugated with coarse transverse ridges on the digits, corrugated with papillary ridges, nodular with papillary ridges, and hairy with coarse transverse ridges and smooth pads. Of these the species with smooth epidermis and hair are few and unimportant, and the largest group examined was that of the Primates, thirty in all, in which papillary ridges were always present. It is highly probable that the causes of these modifications of the epidermis in diverse groups of animals could be traced to the habits and modes of life of each, but I make no attempt here to do this. It is also matter for inquiry, upon which no agreement has apparently been reached, how it came to pass that man has virtually lost his hairy coat, and in regard to the palms and soles of animals, what may be the reason that so few have any hair on them, and why man has no sebaceous glands, but has very numerous sweat-glands in these regions.

This is all of great interest, and possibly some day the Mendelians will solve for us the mysteries thereof. But here I need only ask how it would have been possible for hairs to grow, or, if growing, not to be promptly worn away on a surface used by animals from monotreme to man for walking-pads, and by most of them also for grasping and discrimina­tion between objects as well. We are so familiar with the thickening of the skin on the hands of manual workers and on the feet of those who walk much, to say nothing of what we call a “corn,” from pressure of tight boots, that we are in danger of forgetting that the protecting skin over the hands and feet of animals was of necessity adjusted in a crude way to the measure and kind of walking in past ages and in all levels of life, and that it is maintained in that adjusted condition by the use, or disuse, of each life. Another familiar example is that of knee-pads, as in the gnu and other ungulates. Some such process it is legitimate to assume whether it be reckoned backwards to monotremes or later levels of life-forms. We see then before our eyes how this living tissue becomes adapted in varied ways by response to the stimuli of friction and pressure, and the modifications thus slowly effected must, one would suppose, be transmitted to offspring ultimately from the original groups with which the process began, when by frequent repeti­tion small changes of structure have arisen at last. I acknowledge the limited force of the answer, that this picture involves the continuance in each succeeding genera­tion of the stimuli which initiated the changes, but the fact remains that ex hypothesi the changes are there, written in tablets of animal tissue, and that the making-up of an organism in course of many ages is not and cannot be conceived as being governed alone by the “tyranny,” even in the good Greek sense of that word, of rigid unit-characters.

In the assumed process the correcting force of the Lamarckian drill-sergeant is always at hand, as it superintends the construc­tion of tissues and parts, and I doubt if even Professor Thomson will here interpose the difficulty of “correla­tion with useful characters,” for the only important functions which are invoked as the invariable antecedent of these structures are the elementary habits of walking, climbing or grasping objects in certain different ways, and without these habits or functions there would be neither lemur, monkey nor man to interest the mind of a biologist from Mars. As I am desirous of condensing such replies as I can make to certain opinions of opponents and objections, I will remind the reader that Professor Bateson in the Jubilee Volume of 1909, pp.100, 101, uses a metaphor to illustrate his view that among the facts of nature we meet certain definite structures and patterns in which we ought not, if desiring rightly to interpret them, to expect to find purposefulness. He says: “Such things are, as often as not, I suspect rather of the nature of tool-marks, mere incidents of manufacture, benefiting their possessor not more than the wire-marks in a sheet of paper, or the ribbing on the bottom of an oriental plate renders these objects more attractive in our eyes.” Metaphors are both indispensable and delightful, they are the very salt of scientific and other sober writings, but they have a rather “slim” way of betraying their employers. They express at times the truth too well, and at others when vague and inaccurate lead the reader right astray. Thinking of this metaphor of tool marks I was in a modern church the other day and saw just before me a stone pillar the pediment of which was marked with oblique parallel marks of a mason’s tool. Here then there were marks left by a human hand at some date or other and by means of some tool or other. I know one may not reason by an analogy from inorganic to organic phenomena in which the push and force of life is in full blast, and that inheritance in the former is ruled out; but, taking the metaphor seriously, you have to account for the appearance of the ribbing of paper and the mason’s marks on the stone. To call them “by-products” or “tool marks” or obiter facta, or by any suggestive name, does not advance the reply to the question, “Whence came this great multitude?” If I were unwary enough to be here trying to attack Selection and to respond to the invita­tion of the more learned arachnida to walk into his parlour with a scheme of organic evolution for him to demolish at his leisure, I should have to enter upon the question of adapta­tion, specific difference and perhaps other great disputed doctrines. But, knowing my own limits, and desiring to keep to the self-imposed limits of the title of this book, I again plead that I am here contending, as all through it, for the origin of initial modifications by use and habit, and for nothing else. No one who reads of the immense amount of research and learning that are being carried on by the students of Mendelism and Mutationism can fail to admire them. But, as I have remarked before, these are systems of thought which in the main deal with characters by distribu­tion or “unpacking,” as it is called. Such a process of course leads to new characters by amphimixis, and no one of whom I know denies it. Such work is concerned with fresh views of the origin of species, but with lamentable cowardice, or humility, I leave all that great sphere to those who are incomparably more fit for it, and just seek to mind my own business.

In subsequent chapters on modifications and their origin I shall not need to repeat these observations.

The facts then of a few selected examples of the palms and soles of mammals are shortly these.

A heavy, burrowing animal, the earth wolf of the Cape, has a very smooth, hard epidermis covering its foot-pads and is thus a generalised structure which I have found in no other animal.

The common mole which uses its broad strong fore-feet like a pair of spades, and depends chiefly for discrimina­tion of its habitat on the delicate sensory nerve-endings of its snout, has a hard nodular skin which is much less developed on the hind feet than the fore feet, the latter being less active tools. It has no papillary ridges, in accordance with this fact, and is a very efficient miner that never practises ca’ canny, as we know to our cost when we go out in the morning and find great heaps of soft earth thrown up in the line of its advance from its base or fortress. Such a mode of life lends itself remarkably to the kind of skin on its feet, and this is now at any rate adapted to its environment.

The capybara is a large, heavily-built rodent, and has rather a smooth epidermis not specially thick, with long and efficient papillÆ of the corium shown in microscopical sections. Being largely aquatic in its habitat, and given to frequenting marshy ground and to enjoying as much sleep as it can manage, it depends a good deal for discrimina­tion of objects on its sensitive corium, and its epidermis is not much specialised for, or by friction and pressure in walking. It does not acquire by reason of stimuli and response any unnecessary tools.

With this may be classed the echidna or Australian ant-eater which has sparse hairs set on a hard and slightly corrugated epidermis, and, being mainly a nocturnal animal and living a secluded life, it does not walk much or far in its stealthy pursuit of worms and insects, and the stimuli of friction or pressure encountered by it are few.

A similar condition is found on the feet of many small carnivores.

Animals with scales on their feet, which are held to constitute the earliest stage of the Primate modifica­tion of papillary ridges are such as the potoroo, wallaby, kangaroo and giant ant-eater. Such scales register a long, long series of stimuli of friction and pressure in these and their ancestors, in a level of life before any delicate discrimina­tion of surfaces came into operation.

The nodular form of skin is present in the Canadian tree porcupine, where rough nodules cluster closely on the surface of both feet, and it is a significant fact that it shares with the American opossum the peculiarity of nodules on the ventral surface of the powerful prehensile tail. This adapta­tion tends to efficiency in its arboreal life, and may well have been produced by infinitely small degrees of response in structure in the course of a long evolution.

The rabbit alone have I found with rod-like projections of the epidermic cells, among which are set in dense order the soft, long, delicate hairs and which thus conduce to its wonderful power of treading on sharp objects without injury. We thus see the inner meaning of dear old Brer Rabbit’s jeer of triumph to Brer Fox, “Born and bred in a brier bush.” This adapta­tion might be an unit-character segregated from the ancestral stock of the LeporidÆ, or it might not, but at any rate the rabbit leads a life in which its walking or running is no more prominent or frequent than is a good “run” on the part of a hunter which pursues the hare with his beagles, and one may say at least this—that its mode of life has not produced a hard rough nodular surface on its feet by stimuli of pressure and friction and response.

One may observe that there’s a divinity doth shape our ends, rough hew them as we may, even if some objection be taken to the present view of rough-hewing of parts of our organism on the ground of its piecemeal character, rather than dealing with the organism as a whole. To which it may be replied that the Mendelians give high support to the piecemeal study of the profound subject of genetics, and further that the business here is to look separately and simply at a few selected attributes of parts of an organism, and see how they began to grow big enough to avoid passing through the meshes of the sieve.

The foregoing examples of animals in which papillary ridges are absent have been given not in their zoological order, nor as representative of a great many groups, but as taken from the eighty-six species I examined myself. The following belong to the same series, but all present papillary ridges in an ascending scale towards perfec­tion in man.

Examples of Ridge-covered Palms and Soles.

The common hedgehog though a burrowing animal like the mole is not always underground as his distant relative is. He is not always mining and though of ancient lineage he is a “slacker” compared with the mole, hibernating for months, and spending also much time in his nest and prowling slowly about above ground for insects. He has thus acquired his somewhat indifferent epidermis that one finds, but with the addition of sparse papillary ridges. It is the species among this list with the fewest of these tactile structures, for there are but three or four separate ridges on six of the ten digits, and radiating groups on only three of all the palmar and plantar pads. So qu touch it is ill-equipped, though it has adapted a higher form of tool than the rabbit.

The common squirrel, that sits much and walks mainly on branches of trees just as much as it needs to do, has an epidermis little differentiated, and one which is corrugated with scanty papillary ridges on the palmar and plantar pads, and none on the digits.

The squirrel-like phalanger which flies always more or less downwards by a kind of parachute-arrangement has most of its palmar and plantar skin covered with papillary ridges encroaching upon its corrugated areas, and a response to more delicate tactile experience has been thus produced by its intermittent performance of ordinary progression.

Azara’s opossum presents about as large a part of the surface covered with nodules as with papillary ridges, the latter highly-developed for an animal so low, zoologically-speaking, but one in which delicate discrimina­tion is much practised.

The kinkajou, another arboreal animal which walks about on trees more than it uses its feet for prehension, trusting much to its prehensile tail, shows its corrugated epidermis and papillary ridges developed in about equal proportions.

These five mammals thus show that the stimuli of pressure and friction and the response to them are being complicated by the addition of the more delicate tactile organs known as papillary ridges, and these, perhaps, in a secondary way are becoming useful in preventing friction. But I must not omit to point out that, qu preven­tion of slipping, the few sparse papillary ridges of the hedgehog, squirrel, kinkajou and flying-phalanger, especially those on the extreme tips of the digits, could have no effect in this preven­tion and no survival value. It is otherwise when they are developed in large areas as in the succeeding groups.

Primates.

All the thirty species of Primates possessed papillary ridges to such an extent that only small areas of the palmar and plantar skin of the lemurs showed any other than these remarkable characters. It is so much a property of the Primate hand and foot to possess these that it might be almost made a matter of ordinal rank belonging to the Primates, were it not that a few stray lower mammals also possess it.

The black-headed lemur is the lowest Primate examined and it is characterised by highly developed patterns of ridges on the palm and sole, and these are interspersed with nodules on the regions less exposed to pressure. The complexity of the patterns of another, the ring-tailed lemur, is greater still. Now these nodules are distinguished from the rough undifferentiated nodules of lower forms, such as the Canadian tree-porcupine, and from the scales in others. When examined with a lens the separate nodules show small groups of papillary ridges two, three or four on each nodule, arranged in a direction parallel to those of neighbouring nodules. They are in fact papillary ridges in embryo, and shortly above this lemur-stage in the ascent of animal life they are merged into papillary ridges in patterns. All this is well told at length by Dr. and Mrs. H. Wilder Harris. I refer to it here because the disappearance of the rough, plain, nodular or corrugated epidermis in mammals is coincident with increasing activity and intelligence in forms who employ or acquire a more delicate sense of touch in their hands and feet. The cruder response of structure to stimuli of friction and pressure, evident in the lower forms, is abandoned in the higher, as tactile delicacy in prehension comes more into play. Here, for example, may be a subtle case of the co-operation of the mould and sieve in action.

From this lemur-level the degree of development in the Primate palm and sole rises and falls, but always advances through the lemuroidea, monkeys and anthropoid apes to man. No attempt at the tracing of the lineage is made here, and from the present limited point of view little remains to be said about different Primates. Only two of those examined will be briefly referred to, the slow loris and man.

The slow loris shares with many monkeys and apes a very soft moist skin of the palm and sole, and in this and other refinements of this region it is much beyond many more intelligent, active and higher Primates. I have never had social intercourse with a loris, but I have shaken the friendly little hand of a chimpanzee with a combina­tion of pleasure, mild shock and perhaps memories of my own palms in the more nervous moments of early life. It is a strange, cool, soft and damp surface, but the sensation conveyed by the skin of a loris lately dead show that in life it is a wonderfully sensitive and tender structure. The whole of the palm and sole is covered with well-developed patterns of papillary ridges especially on the palmar and plantar pads. No trace of old-fashioned nodules, scales or corruga­tion is to be found. The structures due to stimuli of friction and pressure in its ancestors have disappeared for ever from this specialised and small group, and we may fairly hold, in accordance with the law of conserva­tion of energy, that the past is somehow enwrapped in the present in the strange hands and feet of the loris. The adaptations of the hand and foot of the loris are most obviously now of value to it in its wary and dangerous life in the branches of trees, but are equally unfitted for that higher life which, in his case, consists in going lower down, on the ground. The extraordinary deliberate life of the loris has been often described. As he moves from place to place on a branch, fixing one limb before he moves another, much as we do in going up a ladder, he is subjected much to the stimuli of pressure, but hardly at all to those of friction. He sets us a good example of leaving nothing to chance. Thus his soft sensitive skin suits well his mode of progression, but he would find the harder, rougher skin of an African baboon very inferior for the purpose. Here, indeed, I have ventured on the edge of Tom Tiddler’s ground, and the Pan-Selectionist or Mendelian will make a grab at me so that I escape with just the loss of a portion of clothing. After escaping I have only to observe to him as to the adaptations of a loris’s hand and foot that in human life, of which we know a little, one can in a measure forecast what a man will be like if we are told on reliable authority what he and his ancestors have not done in the way of muscular or cerebral output, without informa­tion as to what he has done. This is too obvious, but also too complex to prove here by numerous illustrations and it may be left as a mere sugges­tion as to the past life of the loris and his ancestors for many generations. He has not walked in the ordinary method of terrestrial mammals, he has always moved very slowly about the branches of trees, he sleeps most of the day in a hollow of a tree, curled up like a ball, and his home is in moist, tropical regions. No habits and conditions of life could be better calculated to soften and moisten the skin over his palms and soles or expose it less to stimuli of friction, while even those of pressure in his tenacious grasp of boughs are decidedly intermittent. Unless one may assume the appearance in the distant past of some unit-character of soft, moist skin in this and other Primates, it seems difficult to refuse the Lamarckian claim of long, long absence of effectual stimuli of friction and equally long presence of enervating “negative” conditions. Proof of such a view is, of course, wanting.

Palm and Sole of Man.

The palm of man’s hand is a miracle of adaptations for touch and grasping, but has lost most of the coarse structure formed in response to stimuli of pressure and friction which we saw were common in lower mammals. This indeed he shares with most simian forms. The skin of our hands is now very much what we make it and responds very soon to fresh positive or passive conditions. The horny, cracked epidermis on palm and digit of the old sailor may be contrasted with the soft and flexible and pale surface of his twin-brother, the bank clerk, who is of studious habits and has neither the vice of gardening nor golf. If one compares the hand of the ordinary maid with that of her mistress the difference is striking. But if one compares the hand of that mistress with that of her spinster sister who has lain for twenty years in bed or on a couch, the difference is equally significant. Indeed the sofa-and-bed-ridden invalid, of whom I knew a few once, but who have gone out of fashion, gives the observer some useful thoughts as to the why and wherefore of the strange skin of the hands of the slow loris previously referred to. And if he be disposed also to the pleasant pursuit of moralizing at the expense of others he will feel led to reflect over harshly on the invalid and compare her outlook on life with that of the loris. Even in this concrete case of the hand of an invalid there may be evidence of positive as well as negative response, if one examines the right forefinger so much used in sewing, where the skin becomes hard and thick.

The foot of man has a good deal of negative evidence in favour of my conten­tion as well as positive. As to the latter, in the thickening of the skin over the heel and ball of the great toe in those who walk much we find changes precisely similar to those on the hand. The negative or degenerative changes visible on man’s foot consist chiefly in the remarkable simplicity of pattern of the papillary ridges as well as their flattening and blurring, through wasting of those which occupy mainly the arch of the foot. These will be shown in the next chapter in a drawing. When this portion of skin is compared with that of the foot of any monkey or anthropoid ape it is clear that in this respect the skin of man’s foot has undergone even more degenera­tion than his hand has shown of higher development. This degenera­tion has coincided with two facts, first that man’s terrestrial locomo­tion has advanced far beyond that of any other Primate, and second, that he alone has a plantar arch. This subject belongs to a later chapter and is referred to here because the possession of an arch to his foot has caused man to escape, on the under surface of it, a vast propor­tion of the stimuli of pressure and friction involved in his mode of walking, and the extreme simplicity of his plantar papillary ridges, and relatively thin, soft skin under the plantar arches affords a fairly conclusive example of change of structure from disuse per se.

I have thus only selected and used two striking types of the Primates, the loris and man, not wishing to burden this part of the subject unduly with intervening and less characteristic forms of life. It may be legitimate here to say in defence of this long chapter that it illustrates what I desire to keep before me all through, the fact that use, habit, environment and selection go ever hand in hand. In all matters of science one has to descend to particulars, so it seemed necessary to select a few scattered phenomena in the best known groups of higher animals and endeavour to understand how certain “characters” or better “modifications” began to grow big enough to avoid passing through the meshes of the sieve.