the vital importance to the animal evolution of the world in general, and to the welfare of man in particular, of this step forward. It was followed by great changes in the insect world, by the rapid production of herbivorous mammals endowed with speed, great migratory powers, special dental and other anatomical adjustment to the new foods, and the institution in their herds of a discipline, subordination, and leadership which are almost tribal. These last qualities were rendered doubly necessary by the consequent rapid development of carnivora, and the need for scrapping passive and even active means of defence in order to secure the power, speed, and reserve necessary to follow their food harvests over great stretches of country. At the same time the habits and instincts thus brought about were those which man, by domestication, has been able to turn to his own ends. Thus at a blow, as the outcome of this stage of Tertiary evolution, there became available for mankind not only his chief plant food and drink, his luxuries as well as his necessaries, but his chief animal foods, together with his aid from the speed, strength, service, and endurance of the animals which he domesticated and to which he assumed the position of leader of the herd.

But while with the aid just described it was possible for mankind to progress far on the road of civilisation, progress would have been stopped, and as a matter of fact was seriously retarded, until the discovery and utilisation of the solar energy stored up in the earth's crust during the Carboniferous and subsequent Periods in the form of coal and other fossil fuels. The very exceptional conditions, climatal, geographical and botanical, requisite for coal formation, occurred all too seldom in geological history; but it has so happened that few areas of the earth are devoid of coal belonging to one Period or another; and the shaping of kingdoms and dominions has been such as to include supplies of fuel in most of them. Whatever may be the main sources of energy in the future, radiant, intratelluric, hydraulic, tidal, atomic, we have been largely dependent in the past, and probably shall continue to depend for many years to come, on that portion of the solar energy stored up by vegetation, and especially on that preserved in the earth-crust in the form of coal.

But again civilisation must have been greatly hampered or driven into a different course but for the agencies which have sorted out from the medley of materials of which the earth is composed, simple compounds or aggregates of compounds, or in rarer cases simple elements, in such a form that they are available for human use without the expenditure on them of excessive quantities of energy. The concentration of metalliferous ores, salines, and the host of other mineral resources has made perhaps the most important contribution of all to the latest stage-in good and evil-attained by civilisation.

Finally, doubt may be expressed whether man could have attained his present position if he had not made his appearance comparatively soon after a period of intense earth activity, when broad areas of newly raised sediment were available for occupation, when the agents of denudation and renewal were in active operation, and when a wave of rapid organic evolution was active. And a conjecture may be permitted that human evolution itself was probably hastened by the latest climatal severity through which the earth passed, the effects of which are only slowly passing away.

Much of what has just been said may revive recollection of an old Swiss guide-book which praised the beneficence of Providence in directing the dreaded avalanches 'into the desolate and uninhabited valley of the Trumleten Thal and in sheltering from them the beautiful, fertile, and inhabited valley of Lauterbrunnen.' However, it is far from my intention to imply that 'everything is for the best in this best of all possible worlds,' but only to point out, in reviewing the long chain of events of which we see the present end-product in civilised man, that within the ken of the geologist there have been many critical stages in the earth's history when any marked change in the conditions which then prevailed must inevitably have reacted profoundly upon the development of the human race when at long last it stepped out from the lower ranks to take the earth as its rightful possession.

Conclusion.

A review of the history and present position of geology shows that its better-known services to mankind have been in relation to the foundations on which industrial development and modern civilisation have been built -the mineral resources of the earth. These are many and various, all of them explored by geological methods. In every application of them we are again brought back to the primal essentials-water, iron, and fuel— and it is in the discovery and exploitation of these that the services of geology have been of especial value.

But in the course of the development of both the economic and the scientific sides of geology the principles discovered and elaborated have fertilised and enriched human thought as expressed not only in other sciences but also in the sphere of literature. As it has become more precise and is able to give a more accurate and detailed picture of the stages through which the earth passed during the long story unfolded by the study of the stratified rocks, it has shown that the earth, though only a minute fraction of the visible universe, has had a wonderful and individual history of its own. The keynote of this history is evolution, the dream of philosophers from the earliest times, now passed from the realm of hypothesis into that of established theory.

We are able to watch the evolution of the oceans and continents, of the distribution of landscape and climates, and of the long succession of living beings on the earth, throughout many millions of years. During these ages we see the action of the same chemical and physical laws as are now in operation, modified perhaps in scale or scope, producing geographical and biological results comparable with those of to-day. Hutton and Lyell discovered for us in the present a key to unlock the secrets of the past; the history thus revealed illuminates and explains many of the phenomena of the present.

And the outcome of it all is to endow man with a simple and worthy conception of the story of creation, and to fill him with reverence for the wondrous scheme which, unrolling through the ages, without haste, without rest, has prepared the world for man's dominion and made him fit and able to occupy it.

I desire to express my thanks to Mr. G. W. Lamplugh, Professor E. W. MacBride, Professor W. G. Fearnsides, and Mr. G. S. Sweeting for kind assistance in the preparation of this address.

SECTION D.-ZOOLOGY.

CONSTRUCTION AND CONTROL IN

ANIMAL LIFE.

ADDRESS BY

PROFESSOR F. W. GAMBLE, D.Sc., F.R.S.,

PRESIDENT OF THE SECTION.

666

"What like was

It had a

But what was the creature like?" I asked.
it? Gude forbid that we suld ken what like it was!
kind of a heid upon it-man could say nae mair.”
R. L. S.-The Merry Men.

If I were asked to point out the main change in zoological thought since the last meeting of this Association in Canada, I should venture to say that zoological problems have become problems of control, and that control, from implying mere restraint, has come to mean quickening.' The being, well-being, and becoming of the animal in its world are no longer problems of statics, but of dynamics. The fabric of the animal body characterised by those traits and that orderliness that are revealed by genetic analysis is no longer regarded only as a link in the chain of organic affiliation, nor as a fact simply, but as the balanced result of controlled becoming or development. The factorial hypothesis and its corollaries convey this impression strongly. The results of ecological analysis, meagre as they are as yet, point to the same conclusion. Experimental morphology may be summed up in the word 'regulation.' Animal physiology shows the same dominant tendency. The results of tissue-culture show the existence of a process which enriches the body by enforcing it. The infinitely varied animal fabric appears to be the exquisitely balanced individual expression of processes that quicken and restrain.

This change from the older thought of the animal, as a mellowed, balanced product of changes under stress, has come from the renewed hope of understanding the natural problem in the new light of experimental analysis. If to succeed is to come up from below, the actual animal life that succeeds must be but a fraction of the submerged recessive life that experiment reveals. These recessives when artificially bred are no mere cripples, nor disconnected with the evolution of normals. They show us something of the depths of animal nature, and help us to realise that but for the grace of organic regulation we should be even as they. But the study of such analysis as a branch of zoology leads to an even more striking result. Not only does it reveal the existence of these sub-normals, but also it accounts for the defection of certain expected offspring. There are non-viable combinations of living substances. These entering the egg that should by expectation produce a male, render the egg incapable of

development. That family will be one of daughters only. The existence and the control of lethal factors is one of the most significant discoveries of the underworld.

It is with the results of one branch of this experimental study that I wish to deal. For several years experimental morphology has been actively pursued by zoologists in Europe and America. For the most part the egg has been selected as the natural point of departure, and the construction of the embryo or the development of the egg and of its parts has yielded results of great interest, though the search for a principle of organisation has not yet suceeded. To the developing organism it would seem to be all one whether it builds with one egg, with two eggs, or with a piece of an egg. (1) If there be any preformed or self-determined organisation,' it may be shattered to bits without prejudicing the appearance of a normal embryo. The nuclei of the segmented egg may be shaken about as a bag of marbles, yet there will still remain the capacity for normal differentiation. It is therefore not surprising that there is as yet no unanimity of interpretation. Some investigators seek the explanation of development in an innate organisation,' thereby postponing by a process of infinite regress the attack on the problem. Others assume by an unconscious petitio principii the very problem they set out to solve. Others take refuge in a metaphysical solution, and lately the problem of organisation' has been regarded as an ultimate category that stands beside those of matter and energy. (1)

Experimental zoology is a young science, and it is unlikely that we have reached Ultima Thule. Rather than regarding our position as one with our backs to the wall, I would ask leave to consider the report of the advance under the leadership of Professor Child of Chicago that has entered new territory. Instead of attacking the problem of the development of the organism from the egg, Child has long been working at the regulation of regeneration and organic development. From his analytical studies (2) and (3) he has arrived at certain conclusions that have far-reaching consequences. Though based on the behaviour of the lower Invertebrates and Vertebrates, these conclusions have already proved of wide application. I believe I am right in stating that no more fertilising biological idea has been disseminated in the last ten years than Child's hypothesis of metabolic gradients. It has captured the imagination of the younger generation of zoologists and is exercising an increasing influence upon them.

The Individual considered as a Reaction System.

It is no easy task to express the principles of Child's theory of the organic individual without reference to fundamental questions on which differences of opinion prevail, and about which our knowledge is incomplete. Perhaps the best way is to give a concrete instance taken from the freshwater Planarians, those highly organised animated pellicles' that divide by spontaneous fission. This process is initiated externally by a transverse constriction far down the parent body, but without any morphological distinction at this region. The tail-end after separation develops a new head, brain, eyes, and other organs. The head-end develops a new tail, and the process is eventually repeated. On turning up a stone in a stream running through limestone country one can find certain species of Planaria actively engaged in multiplication by this method.

Child's work consisted in applying methods of physiological analysis to this well-known process. He found that before any external sign of constriction had appeared, the intact and apparently single individual showed a hump in the curve exhibiting the rate of chemical change in its tissues, when tested from head to tail. The maximum rate of change occurred in the head region, and then fell off gradually to rise again to a lower peak before the caudal fall. The site of the second, smaller peak was the site of the future constriction, and of the future head of the coming daughter.

From this, and a large number of other experiments, Child concluded that the head of the parent exercised a variable degree of dominance over the subordinate individual that is represented by its own posterior end. External features were no longer the criterion of individuality, but merely the final expression of the physiological relation of dominance and subordination. The nervous system was but one expression of the embodiment of the dominant region (the brain) and of the track (nerve-cords) along which this region exercised its sway. This sway diminished in intensity with the length of the cords or distance from the dominant region, and it was this gradation of the influence of the 'head' on the 'body' according to distance that Child expressed as the 'metabolic gradient.' When the intensity reaches a certain minimum, those portions of the basal region whose potential is rising may assert their own hitherto suppressed individuality.~ They become almost physiologically isolated from the dominant region. The further conclusion therefore arose, that what we are accustomed to think of as an individual multicellular being becomes, when interpreted in the dynamic way, a composite being. The intact Planarian is only prevented from displaying its constituencies by the dominance of the head, but a number of circumstances may interfere with the dominance. As the head by growth of the body becomes removed from the tail region, the intensity of its influence wanes. If the conductivity of the channel of influence falls, the same result ensues. Again, should the tail become the seat of growth, or assert its independence by increase of size or in other ways, then the influence of the head is negatived. In all cases the head action is positive and not merely inhibitory. In all cases the basal action on the head is not positive, but indirect or inhibitory.

'

There are two special assumptions deliberately made by the author of this conception of organic individuality that require emphasis. The first concerns the independent nature of the apical region, the second the use of the term ' metabolic gradient.' The assumption with regard to the first is that the head or apex expresses the most intense and most intimate relation between the organism and its environment localised at one pole. Here the two are really one, and the head is the expression of this fact as a physiological, morphological and historic process. The other assumption is based on the physical basis of life as the seat of chemical changes and chemical correlation in which it is impossible to distinguish qualitative from quantitative effects, and asserts that controlled alteration in the rate of change (for example, of oxygen consumption) along definite gradients is the main cause of that structural and chemical correlation that we call the base. The head or apical region is thus, in a derivative sense, self-determined. It is the animal at its highest; and as these largely

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