Haeckel

The speech at the Scientific Congress in 1863 was the first open confession that Haeckel felt bound to make. But the real work for the new ideas began on his return to Jena. Nothing was further from Haeckel’s thoughts at that time than the idea of becoming merely the populariser of Darwinism in Germany. He has often been spoken of since in lay circles as such. It is entirely wrong. He had the courage to recognise his debt whenever he contracted one; and certainly Darwin supplied the groundwork of his colour-scheme. But he was much too independent and individual in his nature not to take the axe in his own hand at once and begin to hew away himself.

Darwin had strengthened his book with a large amount of the best material that zoology and botany could supply. But there was something else to be done: a theoretical treatment of a general character with cleverly grouped illustrations from the facts already provided by two sciences, and to reconstruct these sciences from their foundations on the basis of the new theory. At that time Haeckel was doing an incredible amount of work, with body and mind. He had an iron constitution. In the year of the Stettin speech he won a laurel crown at the Leipsic athletic festival for the long jump, with a leap of twenty feet. His physical strength seemed so inexhaustible that his host, Engelmann, put a pair of heavy iron dumb-bells in his bed, in case he should want to take exercise during the night. He had a proportionate strength of mind. Everything seemed to promise very well for the next few years, so that he could devote his whole health and strength to the great task of his life. His teaching did not give him very much trouble in a small university like Jena, that was only just beginning to have a scientific name. The happiness of his home life, with a highly gifted woman who shared all his ideas with the freshness of youth, began to chain the restless wanderer with pleasant bonds to his place. He, of course, expected to have his sea-holiday in the old way for the study of his little marine treasures, but otherwise he remained quietly in the valley of the Saale. The warmth of genial and most stimulating friendships gathered about his life. With his comfortable material position he set to work on his great task under the best auspices.

He would have had at the start material enough to work upon without Darwin. From Müller’s time he still had another special class of material, similar to the radiolaria, the medusæ.

The ship cuts through the ocean. It rises like a lofty fortress from the illimitable blue plain, with the white clouds on the far horizon. No land has been in sight for days. Yesterday a poor wind-borne butterfly rested on the deck. To-day it is gone, and all is sea. Then they suddenly appear silently in the blue mirror: mysterious discs, red as the anemones on a Roman meadow in spring, golden as the autumn leaves on a dark pond in the park, then blue, like a lighter blue floating on the general azure. They are the medusæ. At one time the ship sails through a whole swarm of them—thousands, hundreds of thousands, millions, a veritable milky way of coloured stars. On the next day they have all gone. No inhabitant of the ocean seems to be so close to it as this creature. The whole animal is only a shade more substantial than the water. You take it out, and try to catch hold of it. It stings your hand like a nettle: that is its one weapon. But it is already destroyed, melted away, a formless nothing. You put it on a piece of blotting-paper, and it dries up into the spectral outline of a shadow, a tiny “fat-spot,” summary of its whole existence.

Yet this soap-bubble of the water is a real animal. Its transparent body is shaped like a bell, and moves through the water by regular contraction and expansion, like the lung in breathing. Where the clapper of the bell should be, we find a stomach, with a mouth for eating, hanging down from the curved upper part. At the edge of the curved surface are many long fibrils that close on the approaching prey and paralyse it by their sting. Then it thrusts it into its mouth and swallows the object into the stomach. The medusa is, of course, a very lowly creature, but it is much more advanced in organisation than the tiny radiolarian. The radiolarian consists of a single cell. The medusa is a cell-state, a community of countless cells with a division of labour amongst them. Some of the cells form the wall of the bell, some the stinging threads, some the devouring and digesting stomach. In this the medusa comes nearer to man than the radiolarian. Some of the cells see to the reproduction of the medusa. Ova and spermatozoa are detached from the cell-community of the medusa’s body, blend together, and thus form the germ of a new medusa. In most cases the process is curious enough. From the germ-cell we get at first, not a real medusa, but a polyp that attaches itself to the ground, a little creature that may be remotely compared to the pretty water-lilies that meet the eye in an aquarium. Then the polyp produces something like a plant that grows buds, the real medusæ; it may produce these out of its substance as buds, and they then float away like detached flowers, or (in other species) it may gradually change itself into a chain of medusæ, of which the uppermost is detached first, then the next, and so on.

Since this peculiar method of reproduction became known, in the thirties or forties, the medusæ were regarded as amongst the most interesting objects in the whole of zoology. They offered an extremely difficult task to the investigator who would care to take up the study of them.

When Haeckel was with Johannes Müller in Heligoland in 1854 he made acquaintance with them for the first time. His artistic eye was caught with their beauty, as it was afterwards with the radiolaria. “Never shall I forget,” he says, “the delight with which, as a student of twenty years I gazed on the first Tiara and Irene [species of medusæ], and the first Chrysaora and Cyanea, and endeavoured to reproduce their beautiful forms and colours.” His predilection for the medusæ never disappeared. At Nice in 1856 he met them again in the Mediterranean. Gegenbaur’s Sketch of a Classification of the Medusæ provided his studies with a starting-point, just as Müller’s writings did afterwards for the radiolaria. At Naples and Messina he completed his mastery of them. When he had done with the radiolaria for the time after publishing the great monograph of 1862, the next task that loomed up on his horizon was the need for a “monograph on the medusæ.” It would be a long time, however, before he could complete the work in any fulness. A work of Agassiz that purported to do it, but, in his opinion, only confused the subject—he disliked both the Agassizs, father and son, and the father became one of his bitterest opponents on the Darwinian question—gave him a negative impulse to the study. He thought it would be best to deal with one family of the medusæ after another in separate monographs, as time permitted. The first of these essays appeared in 1864 and 1865, and dealt with what are known as the “snouted-medusæ” (geryonidæ). The first volume of the complete work was not published until fourteen years afterwards. If Haeckel had decided to work as a specialist he would have had material enough here to occupy him fully throughout the whole of the sixties, and even longer. The keen student of the radiolaria would be succeeded by the equally keen student of the medusæ. More folio volumes would have accumulated, with beautiful plates, such as only the technical student of zoology ever takes out of the library. His name, like that of his friend Gegenbaur almost, would never have reached the crowd.

It was the influence of Darwin that prevented this. His attention was turned in another direction, and we begin to realise the full greatness of his power when we remember that he nevertheless continued with unfailing quality to publish such detailed studies as those on the medusæ.

Darwinian ideas were fermenting intensely in his mind at that time. The most audacious practical and theoretical problems arose from the fundamental theory, and forced themselves on him at every moment. A great deal was sketched in outline in the Stettin speech, but the serious scientific work would have to be begun on his return to Jena, in his view. First, he thought, two features of Darwin’s system must be given a completely new and original complexion. Firstly, the bottom of the tree, where life begins. Secondly, the crown of all terrestrial evolution: the manner in which man is connected with the tree. It was his philosophic vein that settled both points, the philosophy of unity that sought to replace God by natural development, both below and above, in regard to the primitive cell and in regard to man. But the way in which he set about it was very far removed from all conventional philosophy. The whole rigour of his professional zoology found expression in it. And that was really the novelty of it. The same conclusions might have been drawn by any dozen ordinary philosophers, once they got on the right track. Even they could see that, if two and two are four, one and one are two, and three times three nine. Haeckel went very differently, and much more profoundly, to work.

As an old pupil of Virchow’s he applies the cell-theory to Darwinism—in the lower stage. The first living things, the roots of the great tree of life, consisted of a single cell. The logic of the cell-theory itself went as far as this. But is the individual cell the simplest of all living forms? Here there was a long-standing controversy as to definitions. At first the cell was regarded literally as a kind of chamber, like the cell in the honeycomb. Then it was found that the jelly-like, mobile matter within the cell-chamber was the essential element, the vehicle of life. Finally, it was possible to conceive this slimy substance without any firm membrane, without a chamber. Inside it, however, there was always (it was then thought) a thick and hard substance, the nucleus. If that was the fundamental and only really essential form, the Darwinian primitive and initial type of all terrestrial life must have been a similar drop of living matter with a solid central nucleus, a nucleated individual cell.

How could we pass from this primitive cell to the “inorganic,” the “lifeless,” the “dead,” the ordinary matter of stone, metal, and crystal? Haeckel believed that it was possible to make a step in that direction—not theoretically and philosophically, but practically—by showing that there were still living things on the earth that did not come up to the definition of a true cell, things that had not yet a nucleus in their soft gelatinous body. He discovered a number of tiny creatures that had a homogeneous particle of living matter for body, and showed no trace of a nucleus. The nucleus seemed to be the first beginning of an organ. It was altogether wanting in them.

To these most primitive of all living things he gave the name of monera, or the absolutely “simple.”

In these investigations it is very difficult to determine whether one of these tiny drops of plasm has a more or less transparent nucleus or not. It has often been affirmed in later years that these monera of Haeckel’s did not correspond to their description as living things without a nucleus, or creatures that were below the level of the true cell. It is, at all events, certain that there are to-day large numbers of the unicellular beings known as the bacteria in which no nucleus has yet been discovered by the most sceptical Thomas with the most powerful microscopes and best technical appliances of our time. It is the same with the chromacea (chroococci, oscillaria, nostoc-algæ), very lowly primitive plants whose whole body consists of a globule or granule of living plasm. However, here again the question is no longer of the first importance, now that evolution is entirely and generally accepted. At the time we are discussing the method chosen was all-important. Haeckel drew no conclusions without a solid basis. He believed he could give ocular proof of the existence of beings that were below the level of the cell. It was clear, at all events, that research in this department was only in its beginning, and could pour out wonder after wonder before the world recovered from its first fright over Darwinism.

Then there was the other end of the system—man. Here again it was not merely a question of concluding on philosophic grounds that man must have descended from the lower animals. Huxley had dealt in England with the question of man and the ape on the strict lines of zoology. He came to the important conclusion that man differs less zoologically from the highest apes, the gorilla and chimpanzee, than they do from the lowest apes. He proved his point by a technical study of skulls and brains, not from abstract philosophical principles. It could be demonstrated in the museum or zoological institute to any student with some knowledge of anatomy as easily as the existence and position of any particular bone in the skeleton. Haeckel went even further.

He constructed a genealogical tree stretching far below the apes. Next to them came the lemurs. The lemur, the ghostly nocturnal inhabitant of Madagascar, came from the Australian marsupial (kangaroo, &c.). The marsupial came from the duck-bill; the duck-bill from the lizard; the lizard from the salamander; the salamander from the dipneust or mud-fish; this from the sturgeon or the shark, and the shark from the lamprey. Below the lamprey, at the lowest limit of the vertebrate kingdom, was the amphioxus (or lancelet). This must have come from the worm—it was not at all clear how, at that time. And so the series ran on down to the unicellular protozoa, the amœbæ and the monera.

The construction of this tree would have been impossible for one who had not already done gigantic work. The whole of the new system of animals and plants, conceived in the form of a genealogical tree, had first to be sketched in outline. Then the narrower thread that led up to man, the Ariadne-thread of God-Nature, would gradually come to light.

Both ends of the system, the lower one in the monera, the upper one in man, were first thoroughly treated by him in 1865, and in part somewhat later. His exhaustive Monograph on the Monera was not published until 1868. Man’s genealogical tree was privately circulated at Jena in two essays in October and November 1865. They were published in the Virchow-Holtzendorff collection in 1868 (“The Origin and Genealogical Tree of the Human Race”). But in both cases the substance of the work, as an accumulation of facts, is much older. And this work was, of course, only possible in connection with a number of further conclusions: in regard to spontaneous generation, life and death, the crystal and the cell, the mathematical form of organisms, the nature and limits of individuality, the method of research, the new natural philosophy, God, and so on.

It was an enormous programme, with a Paradisaic freshness. Everything was new and great; and all came from one brain. There was only one man with whom he discussed his ideas as they formed, Carl Gegenbaur, who has undoubtedly had a great, if unconscious, influence on them. Haeckel’s grateful recognition of Gegenbaur’s help in later years was endless and touching. “Thou it was,” he writes to him a little later, “that led me to begin my academic teaching at our beloved Jena six years ago, at the Thuringian university in the heart of Germany, that has, like a beating heart, sent out its living waves of freedom and alertness of mind over Germany for three hundred years. At this nursery of German philosophy and science, under the protection of a free State whose princely rulers ever gave a refuge to free speech and have linked their names for ever with the reform movement, the golden age of German poetry, I was able to work in association with thee. Here we built up our common structure of science in the happiest division of labour, teaching and learning cordially from each other, in the very rooms in which Goethe began his studies of ‘the morphology of organisms’ a half-century before, and partly with the same scientific means, the germs of comparative and philosophic science that he had scattered. We have shared with each other as brothers the happiness and the sorrow that came in the hard struggle for life, and our scientific efforts have been so intimately blended and so mutually helpful, through our daily working and talking together, that it would have been impossible for either of us to determine the particular share of each in our spiritual communism. I can only say in a general way that the little my restless and impulsive youth could offer thee here and there is out of all proportion to the enormous amount I have received from thee, eight years my senior, a more experienced and mature man.”

Goethe stood behind the friends as the quiet genius loci, giving his blessing to all who worked in his spirit on the old spot. Nor was the place itself without influence. “Much,” Haeckel writes, “may have been even the outcome of the common uplifting enjoyment of nature that was afforded us by the artistic lines of the Jena hills, as they brought before us once more at sunset the magic of the Calabrian mountains by the colour-harmony of their purple and gold banks of cloud and their violet shadows.”

“What are the hopes, what are the plans, that man, the creature of a day, builds up?”

The words were written by a poet, in his fatal illness, at the spot where the two strong spirits now worked. In the midst of all his hopes and plans Haeckel was struck by a Niobe-shaft. On February 16th, 1864, just on his thirtieth birthday, his wife, only in her twenty-ninth year, in the full force of mind and of love, succumbed to blood-poisoning.

I turn to the thick volume of Haeckel’s Monograph on the Medusæ. Part I.: “System of the Medusæ:” with an atlas of forty beautiful plates: published by Gustav Fischer, of Jena, in 1879. Few people except zoologists with a technical interest in it have ever opened this voluminous work—why should they? It is a heavy work, with dry diagnoses. The author seems to be far away from all general questions, if ever he was, in the utter stillness of his study. This pure accumulation of matter for truth’s sake does not reach the ear of the world. It lays up material for remote days, before which the individual fades away; it is merely catalogued material of the most technical character. Yet, as I turn over the pages, I seem to see a little image from time to time that is almost like the rose-red or golden-brown medusæ in the sterile, illimitable ocean. In truth neither ocean nor book is sterile; but they are grey and broad. And just as the swimming medusa gladdens me in the one, so a little personal trait of the author does in the other. It is in the choice of the Latin names. A little crown is woven that unites æsthetics and science. I find splendid names, invented by the Professor, on all sides. But I notice that his heart was in these things. He has discovered new species of medusæ, and must christen them. As he turns over his Latin or Greek lexicon a ray of humanity steals into the most severe scientific soul at such moments. I read that a disco-medusa is called the Nausicaa phæacum: “I observed the Nausicaa phæacum in April, 1877, at Corfu, on the shore of Phæaca, in the heart of the Nausicaa.” A cyaneid is given the fine name of the Melusina formosa. It is noted, with great regret, that “so fine and classic a name for a medusa” as Oceania must be struck out on scientific grounds. Amongst descriptions of species in a severe scientific tongue that unnerves the timid reader, amongst gonods, styles, perradial bundles of tentacles, and ocellar bulbs, we find, apropos of the medusa, Lizzia Elisabethæ: “As Forbes dedicated the pretty genus Lizzia blondina to a ‘blond Elizabeth,’ I do the same, and wish to honour, not only St. Elizabeth of Thuringia, but also the ‘blond Elizabeth’ of Immermann and my own dear daughter Elizabeth.”

Then, in the middle of the large volume, we find the following passage on page 189. A medusa is given the name of Mitrocoma Annæ. The name was given at Villefranche, near Nice, in April, 1864 This medusa had “a fairy-like appearance” to its discoverer; its tentacles hung down “like a mass of blond hair!” A note to the name tells us that it was given “in memory of my dear, never-to-be-forgotten wife, Anna Sethe. If it is given to me to do something during my earthly pilgrimage for science and humanity, I owe it for the most part to the blessed influence of my gifted wife, who was torn from me by a premature end in 1864.” In the Art-forms in Nature, Haeckel’s work of 1899, we find a medusa Desmonema Annasethe similarly—after thirty-five years—apostrophised: “The specific name of this pretty disco-medusa, one of the most beautiful and interesting of all the medusaæ, immortalises the memory of Anna Sethe, the gifted and refined wife (born 1835, died 1864) to whom the author of this work owes the happiest years of his life.”

If one would fathom the depths of human emotion one must reflect what these words, in such a context, contain; it is the last gentle vibration of a most deep inner experience breaking out into this prosaic, scientific material. A medusa is a trivial, possibly a funny thing, to the layman. The man of science looks deeper into it, and sees a wonderful revelation of nature; the eye of Goethe’s God shines on him from it. But when he has devoted years to the most careful study of it, it assumes also a naïve individual interest for him, as the companion of his solitary hours of observation in the heart of nature, far from all the whirl and bustle of the world. Only the deepest and most intimate feelings break out in such moments. And here they have left their monument—in a Latin name that science will go on coldly entering in its catalogues for ages to come. It seems to me that this simple fact tells us more of the character of this true-hearted man, in whom nothing human was lacking, than long narratives could.

When the aged Sethe saw the break-up in 1806 of the State of Prussia, in the invulnerability of which he had believed as a gospel, he sought refuge in the comfort of work. “I succeeded in benumbing my mind: I experienced in myself that hard work is a soothing balsam, co-operating with our tardy healing force.” The grandson, wounded in a more terrible way and cut to the very heart, tried the same remedy.

Thirty years afterwards, when crowns were prepared and speeches delivered in honour of Haeckel’s sixtieth birthday, when the whole of Jena fêted him as their own, and the veil fell from his marble bust in the Zoological Institute, to which seven hundred of the best known names in German and foreign science had contributed, the hero of it all went back to that dark hour. “I thought at the time that I could not survive the blow, thought my life was closed, and purposed to bring together all the new ideas that Darwin’s theory of evolution had evoked in me in a last great work. That was the origin, amid bitter struggles, of the Generelle Morphologie. It was written and printed in less than a year. I lived the life of a hermit, gave myself barely three or four hours sleep a day, and worked all day and half the night. My habits were so ascetic that I really wonder I am alive and well before you to-day.”

In his hour of collapse Haeckel sat down and wrote “the book of his life.” There were only two alternatives for a book written in such circumstances. It would be either very bad or very good. When a young man in his thirties throws himself into a great effort of this kind and writes a work that he conceives as a testament—a work in which he will speak for the last time, but will say everything—it is a desperate test of all that he has done in his three decades of life and is about to give to the world. In this case the test succeeded beyond all expectation.

The General Morphology of Organisms^[2] was published in 1866, with the sub-title: “General elements of the science of organic forms, mechanically grounded on the theory of descent as reformed by Charles Darwin.” It consists of two thick volumes of small print, containing more than 1,200 pages. The preface is dated September 14, 1866. It is now one of the most important works in the whole mental output of the second half of the nineteenth century. In respect of method of scientific research it is a landmark by which we may characterise and appraise the whole half-century. For general biological classification it inaugurates a new epoch, as had been done fifty years before by Cuvier, and again fifty years earlier by Linné. What it did for zoology in the narrow sense was thirty years afterwards summed up in one phrase by a writer of acknowledged competence, Richard Hertwig: “Few works have done as much towards raising the intellectual level of zoology.” Among Haeckel’s own achievements, great and varied as they are, this work occupies the highest place. Setting aside certain special pieces of research, and regarding him mainly as a man of great ideas, we find his whole programme in this work. The History of Creation, that has taken his name far and wide over the globe beyond the frontiers of zoology, is only an extract from this work. He put his heart in it. The others are only the improved blood-vessels of his system of ideas, partly duplications, partly simplifications. I do not say this either in blind admiration or in criticism, but as the expression of a plain fact. Posterity will turn to this work when, either in hostility or in sympathy, it wishes to appreciate Haeckel.^[3]

His contemporaries did not accept the work without difficulty. It came out without noise, exerted a tremendous influence in a quiet way, and at last disappeared altogether from the bookshops. It is still attacked, but has never been refuted. At libraries one finds, as I know from experience, that it is always “out,” and therefore must be read continually. It is found occasionally at second-hand booksellers; an antiquarian price running to five pounds and more is put on it, after forty years’ active production on the part of its author. At present you could count on your fingers the German works that have this distinction of being highly priced and out of print. One such is Vischer’s Æsthetics, and another is the first edition of Gottfried Keller’s Green Henry. Keller had threatened any one who ever attempted to republish this first edition (afterwards modified but not improved by him) that their hand would not rest quietly in the grave. But the price of the work went up amongst antiquarians. I feel, in speaking of Haeckel’s General Morphology, that I am describing a book which has become so rare that one must treat it as something new, a codex that is only accessible to a few. It is certainly not known to the general reader.

Let me endeavour in a few words to give a general idea of the chief contents of the work.

All the intellectual forces that had had any influence upon Haeckel now concentrated for a supreme achievement. First of these was Goethe, who supplied the title, “Morphology.” In its simplest signification morphology is merely “the science of forms.” If I take houses, furniture, statues, fishes, flowers, crystals, &c., and only regard and describe their forms, I am a morphologist in the literal sense of the word. But when Goethe invented the term he sought to give it a more restricted application, writing in the style of earlier days, but clearly enough, at Jena in 1807. We have, he says, natural objects before us, especially living objects. We try to penetrate the secrets of their nature and their action. We are not merely observers, but philosophers. It is from this point of view that we approach the subject. It appears to us that the best way to proceed is to separate the various parts. Such a procedure seems calculated to take us very far. Chemistry and anatomy are instances of this analytic kind of research, and both are greatly esteemed and successful. But this method has its limitations. “We can easily break up the living thing into its elements, but we cannot put these together again and restore them to life. We cannot do this in the case of many inorganic, to say nothing of organic, bodies.” What are we to do? “Hence,” Goethe continues, “even scientific men have at all times had an impulse to recognise living things as such, to grasp connectedly their external visible and tangible parts, and take these as indications of the inner life, and thus in a sense to compass the whole in one glance.” “Hence we find at the threshold of art and knowledge and science a number of attempts to establish and elaborate a science that we may call morphology.”

Perhaps Goethe’s meaning can be realised best if one takes a great work of art—say, the Venus of Milo—and imagines how these different kinds of knowledge would deal with it. Purely analytic anatomy would dissolve the superb artistic form into a rubbish-heap of bits of marble. Chemistry would still further break up these bits of marble into the chemical elements of which every block of marble is ultimately composed. The “form” would disappear altogether. But in this case the form means—the Venus of Milo. We see at once that we need another branch of science and investigation besides anatomy and chemistry: we need a morphology, or science of the complete form in which the block of marble is moulded into the Venus of Milo. In the case of our work of art, morphology would be identical with æsthetics, or at least with a branch of it. There can be no doubt that the first and most imperative need for the establishment of a special science of morphology arises from artistic and æsthetic feelings. It is not without significance that it was founded by the poet Goethe, and elaborated with such great success in the nineteenth century by the born artist Haeckel. However, that does not prevent the analogy of the Venus of Milo, which happens to be a creation of human art, being applied equally to every individualised form in nature, to every crystal, plant, and animal. Goethe himself immediately transferred his morphology into the province of botany with such vigour that the term is still regarded, in its narrower sense, as a technical botanical expression. It extends, however, to the whole world in so far as its contents come before us in “forms.” When Haeckel adopted the term he deliberately restricted it, in harmony with the general definition, by calling his work the “Morphology of Organisms,” or the science of the forms of animals and plants.

But there was one danger in the conception of a morphology of animals and plants, namely, the danger of taking it to mean a purely external description: so many thousand species of plants, soberly described, labelled, and numbered, a huge cabinet of stuffed skins, a herbarium of hay. A whole scientific school had really taken it in this sense since Goethe’s time; much as if one were to think æsthetics consisted simply in forming an illustrated catalogue of all the art-treasures in the world, a realistic catalogue in which the marble statues from the Parthenon and the Moses of Michael Angelo would simply be given as number so-and-so in class so-and-so.

Haeckel was preserved from this school by his more immediate masters, as well as by Goethe himself; firstly by Johannes Müller, then by the botanist Schleiden, finally by the influence of Gegenbaur. There was at the time enough, and more than enough, of this external museum-morphology. It was far from Haeckel’s intention to produce a new compendium, in several volumes, of this kind of science of plants and animals. His morphology was to be “general,” to have a broader range, be a programme. As Richard Hertwig said very happily at a later date, he saw his science, not as it then was, but as it ought to be, in his opinion.

The science of forms was to be in the fullest sense a “philosophy of forms.” “Zoological philosophy” was the name given by the hapless Lamarck, in France a century ago, to a work that appeared in the year that Darwin was born, and anticipated his most advanced thoughts. Haeckel, also, gave a new “philosophy of zoology and botany.” The title embodies the magic formula that gave him courage to take up resolutely once more the proscribed word, that seemed to have been scalded and spoiled for ever in the witches’ cauldron of “natural philosophy”; it spoke of the “theory of descent as reformed by Charles Darwin.” Two sub-titles divided the work into two sections from the start. The first part was, the critical elements of the mechanical science of the developed forms of organisms (animal and plant); the second part was, the same elements of the mechanical science of the developing forms of organisms.

In these titles we see the decisive advance beyond Johannes Müller. As Goethe had already declared, morphology as such can be formed into a real and profound science. It will then not confine itself pedantically to a registration of forms. It will compare them with each other, and seek the hidden law in the straggling phenomena. It will mark out broad lines that will enable the human mind to grasp its objects in all their fulness. Johannes Müller had only been able to confirm that in the narrower sphere of biology. This was the nerve that gave vitality to zoology and botany, and made them a province of the mind in the higher sense. But the question now was: which laws were detected, and in which category of thought were they to be found? Müller had the theory, but was weak on the practical side. There were the “forms” of animals and plants. What was it that really connected them? What was the reality that corresponded to the philosophic craving of the intelligence? Müller’s next school, the generation immediately preceding Haeckel, that of Du Bois-Reymond, Virchow, and many others, had apparently indicated the solution. They had replaced Müller’s vague general conception of the laws of morphology and life, which was undermined by older influences, by a single great demand. We want to grasp nature as a unity. At one point in nature we have reached deep and apparently fundamental factors—in physics and chemistry and their plain natural laws or forces. Now let us try, starting from the idea of unity and from the plainest of all philosophical principles, that of proceeding from the known to the unknown, to reduce the forms and phenomena of life to these natural laws of chemistry and physics. Let us find out whether the whole form-world of the animals and plants—in other words, the whole province of morphology in the narrower sense—can be traced to the same natural laws that we have in chemical and physical phenomena. The globe is the object of chemistry and physics. Shall these few green or other-coloured things that lie at the limit of the air, water, and rocks, a small minority in nature, the things we call animals and plants, alone in the whole world be exempt from the action of these laws? It is immaterial that Müller’s best pupils, Du Bois in his later years and Virchow at an early date, departed more or less from this consistent position of theirs into philosophic and other sidepaths. The younger generation, to which Haeckel belongs, that only came into direct touch with Müller in his last years, heard no other gospel. What further advance was to be made? In chemistry and physics they had before them the deep stratum that yielded good mechanical laws. The first stage of physiology after Müller, as we find it, for instance, under Du Bois-Reymond, yielded some good indications for the organic. But was the whole of morphology to be remodelled? Was the vast labyrinth of the thousands and thousands of animal and plant forms in the museum to be reduced to mechanical laws, corresponding to those of physics and chemistry, and be explained by them?

Darwin brought salvation. Now that he had appeared, Haeckel felt that he could begin to work. The hour and the man were come.

Darwin made it possible for him to raise morphology to a penetrative science, equal to physics and chemistry, and so to make a step towards the unity of our knowledge of a unified world. Hitherto the morphology of the animals and plants had been in confusion. God, imagined in the form of a higher man, had deliberately created the organic forms, the palm, the moss, the turtle, and the man. He had constructed them on a definite plan, as a man makes machines. Now, it appeared, the deeper stratum was peeping out even here. Laws that had built the heavens and the earth reached, by way of the Darwinian theories of selection and adaptation, to the moss and palm, the turtle and man.

It was Haeckel’s peculiar distinction to take up this path as the right one. It was then altogether new; to-day, even in the eyes of an opponent, it has at least the solid and consistent support of a considerable party. In later years, apart from open deserters from the free and uncompromising pursuit of truth like Virchow, a school of zoologists and botanists has been formed that will not recognise in Darwinism a reduction of vital phenomena to the simple chemico-physical laws of the rest of nature. They look upon it partly as inaccurate in its allegations of fact, partly as a nebulous confusion, if not, as I have already said, as a false mysticism or metaphysic. In the opinion of these critics, whose own confused ideas very often leave little to be desired in point of nebulosity, and who frequently try to drive out the devil by means of the devil’s grandmother (a matter we cannot go into here), Haeckel had made a great mistake in thinking that Darwinism would solve the Du Bois-Virchow problem of reducing all living things to the laws of lifeless matter. Even these, however, must candidly acknowledge that in doing so he was the victim of his consistent and honourable inquiry. At all events he must logically have seen the correct line at that time as it is recognised to-day by this anti-Darwinian but professedly mechanical school. His individual error can only have been that he was deceived as to the true course of the line, and so clung to Darwinism. However, we have said enough on this point.

Haeckel himself, at the time he was producing his greatest work, saw in Darwin the absolute “open Sesame” to all the doors of philosophic morphology. With this Sesame came an entirely new impulse, namely, to write the natural history of the animal and plant form. It was just the same as when æsthetics perceives a new world, a world that alone is worthy of it, the moment it passes from the making of a mere catalogue of the world’s art-treasures to the knowledge of even one single law of artistic creation, in virtue of which one single work of art has been actually built up.

It is impossible to begin with more general considerations than this book does. The method of scientific research generally is explained in order to give an idea of the new Darwinian morphology. With a calmness that must have made most of the contemporary zoologists and botanists shiver, the discredited idea of natural philosophy is restored from the lumber-room. “All true science is philosophy, and all true philosophy is science. And in this sense all true science is natural philosophy.”

The various periods in the development of morphology are coolly schematised. These epochs are characterised by the vicissitudes of the struggle between the simple description of forms in the animal and plant worlds and the philosophic exposition of the laws that lie behind these forms. In the eighteenth century, under Linné, there is a period of purely external description and classification. It is succeeded in the first third of the nineteenth century by a triumph of the philosophic treatment of animal and plant forms. This increases with Goethe and Lamarck, and grows into the older (and now generally abused) imaginative natural philosophy. Then there is a general reaction; with Cuvier comes the least philosophical of methods, though at the time it is a real advance. While Linné only gave an external description of forms and catalogued them, Cuvier’s epoch penetrated to the inner structure, the inner world of forms, and thus rendered great service. The last and greatest workers of the period, Müller, Schleiden, &c., give the signal for a reaction in the hour of its chief triumph. Haeckel now follows this up as “the element of fact in their ideas.” With Darwin he inaugurates the fourth epoch, the triumph of natural philosophy for the second time. But it is now far deeper and clearer; it embodies all the good that preceded, all that Cuvier and his followers have done, without the irresolution of earlier days. Now that we have studied the living form in its innermost structure, as was never done before, in the earliest stages of embryonic development in the ovum and womb, in the past geological periods of the earth’s history, we will think over this form, think with all the means at our command, reason, synthesis—even imagination, when it is necessary to press on to the great final conclusion, a new synthesis of the defective positive data. What does Johannes Müller say? “Imagination is an indispensable servant; it is by means of it we make the combinations that lead to important discoveries. The man of science needs, in harmonious co-operation, the discriminating force of the analytic intelligence and the generalising force of the synthetic imagination.” That is spoken from the depths of Haeckel’s heart, and he drives it home.

Nothing is more amusing than to find Haeckel’s later opponents saying, apropos of any particular question, that his statement springs from his “imagination,” as if it were something wholly unscientific that the naturalist must shun like the pest; or again, that Haeckel here or there falls a victim to the deadly enemy of all scientific research, natural philosophy. It is pointed out to him as a great discovery which he must approach in a proper penitential spirit—to him who has discussed these matters so unequivocally in his first theoretical work.

As a fact, these methodological chapters in the first volume are as clear as crystal. The titles will seem strange to the man who thinks he can do without any philosophical instruction in zoology and botany, and wants to hear only of cells, tissues, stalks, leaves, bones, scales, and so on, in a general morphology. One chapter has the heading: “Empiricism and Philosophy (Experience and Knowledge).” Another heading runs: “Analysis and Synthesis.” Then there are: “Induction and Deduction,” “Dogmatism and Criticism,” “Teleology and Causality (Vitalism and Mechanism),” “Dualism and Monism.” The last three antithetic headings are united under a general title as “Critique of Scientific Methods that are Mutually Exclusive.” Such a title illumines the whole situation like a flash of lightning. Many years afterwards Haeckel himself said of his General Morphology that it was a comprehensive and difficult work that had found few readers. At least the whole of this first and most difficult part of the book must be defended against the criticism of its parent. If it is far from adequately appreciated to-day, especially by professional philosophers, that is certainly not due to its style, which is a model of clearness in the eyes of any one with the least philosophical culture. The real evil was that people did not look to it for instruction from the philosophical side. The title, “Morphology of Organisms,” had a technical sound. The empty space between professional philosophy and professional zoology is wide enough to-day, but it was far wider thirty-four years ago. Books like Büchner’s superficial and popular Force and Matter, or Haeckel’s own later work, the History of Creation, that can only be regarded as a brief and incomplete popular extract in comparison with the General Morphology, with all its peculiar literary charm, stole into the philosophy of the time like foxes with burning straw tied to their tails. Professional philosophers have written whole libraries on them. The matter recalls a fundamental defect in academic philosophy: it has little or no sympathy with real scientific work; in fact, it studiously avoids such sympathy in the consciousness of its own weakness. Hence it has, like every other layman with general interests, to wait for attempts to popularise scientific work before it can know what is going on in the serious camp. The man who wants to-day to criticise the mechanical conception of nature should first make himself acquainted with these chapters of the Morphology. How many know the mere title of the work? How many even of those who evince great hostility whenever Haeckel’s name is mentioned?

The book contains much more than the methodological introduction. This only takes up the first hundred pages, but it contains the whole programme. We start off, therefore, under full sail for a new epoch of thought, for natural philosophy; but we must keep an alert mind. The deeper task, that Darwin only gave the means of accomplishing, was to reduce all living things, animal or vegetal, to the inorganic. The laws of life must be merely certain complications of the simple laws that are encountered directly in chemistry and physics, and rule throughout nature. It must be one of the first aims of a general philosophic morphology to open out a path in this direction.

The living and what is called the “dead” must be compared. Linné’s three rigid kingdoms—animal, plant, and mineral—needed definitions in harmony with the new ideas. Haeckel himself had discovered the “monera,” the living particles of plasm that did not seem to have reached the stage of the true cell. Here, clearly, was the lowest level of the living. At the same time we reach the most complex specimen of the inorganic from the morphological point of view—that is to say, the most interesting in its individual form—the crystal. The differences begin to give way. What marvellously similar functions! From the dead mother-water is built up, purely by chemico-physical laws, the beautiful structure of the crystal. From the lowest living particle of plasm without any special organs, as we see in the radiolaria, are formed the beautiful siliceous frames that Haeckel had collected in such quantities at Messina. Is it more than a hair’s breadth to pass from one to the other? The deeper we go in the study of living things, the slighter become the differences that separate them from “dead matter.” On the other hand, the higher we go in the structure of crystals, the more striking is the resemblance to the living thing. Two chains of thought seem to be started. What we call “dead” is really alive: what we call living is really subject to the same laws as the “dead.” The solution is found in complete Monism. Living and dead are not antithetic. Nature is one; though we see it in different stages of development. We call one of them the crystal, another the cell, or the moneron, or the protozoon; another the plant, another the animal. Historically it all hangs together. The same laws hold sway throughout. In framing my arbitrary definitions I can say either that the dead is living, or that the living does not differ essentially from the dead. In the chain of living things man comes from the primitive cell, the moneron. This in its turn has developed from something earlier—“naturally” developed. The very idea of life forces us to seek the predecessors of the monera. Hence we speak of “spontaneous generation,” as what was dead according to our ordinary use of language has begun to live. In point of fact it is merely development of a unified whole. There is no gap, no leap, no act that is not natural. The dead and the living never were really antithetic.

The insistent statement that not only does the living approach the inorganic, but the inorganic approaches the living, is quite “Haeckelian.” The study of the “life” of crystals is one of the best parts of the book. Later generations will appreciate it. We are much too narrow to-day when we merely reflect that life, even the life of man, can be traced by evolution down to what we call dead matter. We forget that this “matter” is already high, since it potentially contains life, and even man, the crown of life. Many people imagine that the derivation of man from “dead matter” is equal to turning a king into a beggar. They do not reflect that, on the other hand, a beggar is turned into a king. When I say that life arose one day out of the inorganic, or that a crystal was turned into a cell, my statement really involves the complementary truth that the inorganic potentially contains life in itself. Otherwise we have the old miracle over again of something being produced out of nothing, in spite of our spontaneous generation. Haeckel has always been clear on this point. His later studies of the soul of the atom and the plastidule only carry out the absolutely logical treatment of the question that we find in these chapters of the first volume of the Morphology.

Incidentally the question is raised whether the plant or the animal was evolved first. Animal and plant are, of course, not rigidly distinct from each other. They are only the two great branches of the Darwinian evolution of living forms, and are united at the bottom, however much they diverge above. Gegenbaur had represented this years before (1860) in a figure that Haeckel quotes in his Monograph on the Radiolaria in 1862. The whole kingdom of living things must be conceived “as a connected series, within which we find two lines diverging from a common centre and representing a gradual differentiation and development of organisation.” The terminal points of these lines (the highest plant and the highest animal) are very different from each other, but the difference gradually disappears as we go back towards the common centre, and the lowest stages in each kingdom can hardly be distinguished from each other. For these lowest stages Haeckel now carries out a plan that very quickly forced itself on him.

He forms them into a new kingdom of life. To the animal and plant kingdoms he adds the primitive realm of the beings that showed unequivocal signs of the possession of life, yet were neither animals nor plants. He gives them the name of “Protists.” To botany and zoology is now added protistology.

The name “protists” (from protiston, the very first) is familiar to every one in biology to-day. If protistology has not yet been securely established as a special branch of science, that is due to the circumstance that a strict limit cannot be determined on either the plant or the animal side, so that the botanist encroaches on the province at one point and the zoologist at another. But when we remember that Haeckel’s protists include the well-known bacilli, on which whole libraries are accumulating to-day, it is clear that the province must be definitely marked off at some date in the near future, whether one accepts Darwinism or no.

These important innovations in technical biology show very clearly how sound and fruitful the new “natural philosophy” was. We have to go back to the untenable and utterly impracticable systems of Hegel, Schelling, and Steffen, which were immediately rejected as the trifling of dilettanti, or even to much that the admirable Oken did on the scientific side, if we would measure the whole distance between what people understood in the sixties by “natural philosophy” and the real reformed philosophy that Haeckel gave to the world. This becomes clearer at every step we take in his work.

The first book has determined the method that leads to morphology, the science of forms. The second has ranged the organic forms—protists, plants, and animals—over against the inorganic or “dead” forms, as far as this is possible from the new evolutionary point of view. We feel that the third book will pass on to Darwin, and explain the world of organic forms by the Darwinian laws of evolution. Then the programme would be carried out in its main features.

But Haeckel writes two whole books before he comes to this, and they are, perhaps, the most characteristic in the work. He only “adopted” the theory of evolution in the sense that he applied it far more thoroughly than Darwin to practical problems. In these two books he is entirely himself. They are, at the same time, the most difficult in the work. Even to-day they place him on a lofty and lonely height apart from the great and strenuous controversy over Darwinism. I believe that the time will yet come that will fully appreciate these books. Through them Haeckel will play a part in philosophy of which we have at present no prevision.

There is a word that is inseparable from the word “form”—individuality. Morphology, which does not analyse, but studies the form-unities as a whole in the sense of Goethe’s definition, comes from the nature of things to deal with the individual. In our artistic illustration the Venus of Milo, as a form-unity, is an æsthetic individuality. When its form is destroyed, its individuality perishes.

Let us apply this to any one of the higher plants or animals. Take a turtle, for instance. A definite individual embodies the definite form to which I give the name. This form as such is entirely lost if I cut up the turtle until it is unrecognisable. The limit of morphological study seems to be, just as in the case of the Venus of Milo, the integrity of the individual turtle. Yet in the living turtle we find an enormous difference.

If I grind the Venus of Milo into dust, I am at once in a totally different world with this dust. I am amongst the raw material of nature, untouched by æsthetic influence. From this calcareous powder I can, in reality or imagination, pass on to the world of crystals, molecules, and atoms. In that case I shall have done with æsthetic morphology. I come to the morphology of the inorganic, a very different branch. What do we find in the case of the living turtle?

It is true that I can break up the turtle into simple chemical substances. In that case I make the same transition; I abandon organic morphology, and pass, with the same salto mortale as in the case of the Venus of Milo, to the lower science of inorganic morphology.

But when I examine the structure of the living individual turtle before me I notice a special feature. Let us suppose that I break up the Venus of Milo only to a certain degree; or, with less vandalism, I do not break it up, but light up its inner structure to some extent by a sort of Röntgen-ray apparatus. And suppose I found that this one æsthetic individuality is made up of millions of much smaller and æsthetically finer and more unified images. I do not mean of millions of repetitions of the large Venus in miniature, but of real and unmistakable little works of art, each of which, regarded separately and without any injury to its narrower individuality, might be just as excellent a subject for æsthetic examination as the whole Venus.

This is, of course, nonsense as regards the Venus of Milo. There is nothing of the kind in it. I have given the paradoxical supposition merely for the purpose of showing what we really find in the case of the turtle.

When the organic individual turtle is closely studied it breaks up first into so many simpler organic individuals, which undoubtedly belong as such to the province of organic morphology. They are the cells. The theory of Schleiden, Schwann, and Virchow here comes into direct touch with morphology. Every higher animal or plant has its own individuality; and within this individuality there is a conglomerate, a community, or a state, of individuals of a lower order, that have their own life and their corresponding individual life-form. Man himself, the highest of animals, is a cell-state. So Virchow taught. Each one of us is an individual, and as such an object of morphology. The cell, each single cell in each of us, is also an individual, and as such is equally an object of morphology. Hence it is the task of the morphology of organisms, not only to describe these higher individualities as such, but also to look on them as glass-houses, as it were, with so many shelves, divisions, and smaller houses within of a lower rank. These internal arrangements have to be described, piece by piece, with the same fidelity.

This will probably suffice to convey a general idea of the subject. Clearly, the great work that ought to form the general part of morphology at this point was the precise determination of all these various layers of individuality that are found in the animals, plants, and protists, and, as we rise upward, enter into more and more complex relations to each other.

The difference between, say, a turtle or a man and the cell which combines in its millions to form them is not the only one. Between them we seemed to find individualised, or almost individualised, links. Think of the idea of an organ. What is my heart? It is made of a number of cell-individuals, like my whole frame. But these cells form a sort of intermediate individuality in me. We may go further. What is a segment of a worm? What is an arm of a star-fish? They have so much independence that they can continue to live, rapidly producing new cells and forming a new worm or star-fish of the higher individual type, if they are cut off. The arrangement is still more difficult in the case of the plant. Where in their case shall we find the stages of individuality that correspond to the animal-human? The cells are distinct in both cases. The individual plant-cell corresponds to the individual animal-cell. But what is there in the plant that corresponds to me, as the animal-human multicellular individual? Does the oak-tree, for instance? Certainly, the oak is an individual. But it seems that it is the single sprout of it that corresponds to what I am. What is the relation of the tree to this sprout?

Here our ideas grow dim and confused. We human individuals unite to form certain higher communities. The word “social” reminds us of the fact: then we have the nation, the race, humanity. At least the earlier of these stages certainly perform various combined functions, and are understood to form, or wish to form, new individuals. We speak of the social organism, the body of the people, the soul of the people, and so on.

We see that still more clearly in the case of the animals about us. Individuals, that correspond to our conception of an individual man, combine and form stocks and colonies, with division of labour. We find this in the medusæ, corals, anemones, tunicates, and vermalians. One of these animal stocks, to which our human social combinations only correspond in a much wider sense, gives us a stage that is represented by the tree in the plant-world. Infinite perspectives open out, and also infinite complications. Infinite problems spring up for morphology to deal with; it must make its way through the labyrinth of these complicated types of individualisation.

The matter is still more intricate if I begin at the bottom of the biological series and proceed upwards. I, man, am an individual of a certain stage in my own collective activity. It is true that I am made up of millions of cell-individuals, but when we look at the whole these are merely elementary units. But take a being from the protist-world that is too lowly to be either animal or plant. In respect of its whole activity it is an individual just as much as I am, and therefore in this regard at the same stage as I. At the same time it consists of a single cell. The distinction in me between unit and whole does not exist in it. Its unit is the whole. It would seem a Sisyphean task to reduce all this to a system.

Yet that is just what Haeckel has done.

With crystalline clearness he separates and reunites and arranges everything, from the primitive organic individual, that is not yet a true cell—the monera he had himself discovered—upward. Organic morphology begins with them as its first object, the first complete individuality, the first “form.” All that lies below it is beyond the province of morphology. The last conceivable organic individuality is, perhaps, the atom; and that is not the concern of morphology. We start from the organic. Above the pre-cellular individuals and the true cells the next form-unities are the organs. Above the organs, after a few subtle intermediate stages, are the “persons.” Thus a new word is given to what we have hitherto conventionally called an “individual,” when we wanted to denote a turtle, a bird, a man, or an higher animal as a whole. To this corresponds in the plant the sprout. The stage above the “person” is the “stock.” We might also call it the social individual; in the plant-world it is the tree, in the coral the coral-stock, in the human case the social combination of a number of men for common action.

We are reminded of Virchow’s speech, and how “consciousness” was dragged into the debate on the cell-state. What psychological perspectives are opened out by this doctrine of individuality! Each form-unity, each single individuality in the series, with a soul! Souls combining for common action, and forming higher psychic unities! There is no detail in Haeckel’s whole life-work in which he speaks more boldly and freely and philosophically than he does here. His lucid treatment raises to a higher stage a philosophic question that has occupied thinkers for ages.

That is the third book. The fourth takes up a different subject. Let us adopt in organic morphology this wonderful theory of individuality, the theory of stages within the form. Then let us turn to consider impartially the vast multitude of living forms. How can we now arrange this infinite confusion by merely looking at it? Artificial classification has attempted it a hundred times, and always without success. On this side there is only one way to proceed—the mathematical.

I study them with strictly mathematical figures. I determine their axes, and the mathematical aspects of their forms. Possibly that will give a practical result; the only kind of artificial system that can be accommodated with the Darwinian theory, and perhaps render it assistance by the sharpness of its lines. Does it answer? Take a crystal, a specimen from inorganic morphology. The description of it is susceptible of a strictly mathematical form. Now take a star-fish, a worm, a human being. We find that even these organic structures have a mysterious relation at bottom to certain mathematical, stereometric forms. We might almost say, to certain forms of human thought. Everything in the organic world is in a state of flux. But through the whole moving stream we can trace the outline of one stable element, something like a mathematical idea. A sort of Platonism of the living forms vaguely takes shape.

Haeckel speaks of lines, axes, circles, radii, and all kinds of rhythmic structures. It does seem that the countless individual forms of living things fit into a scheme of a limited number of mathematical forms. Strictly speaking this is not a real morphology of living things. We only find these clear and rigid forms schematically in the wild profusion of forms of the protists, plants, and animals. They are only a reminiscence of the laws of the purely inorganic, which the eye of the observer just detects as the lowest stratum. Hence Haeckel calls this section the “promorphology” of organisms.

It is true that this section, which essays to compress all living things into a very simple scheme, is the hardest to read in the whole work. A number of strange and difficult words have to be invented for this stereometric scheme to which he would reduce the animal and plant forms. Haeckel himself declared, twenty years afterwards (in the second part of the Monograph on the Radiolaria), that this stereometry of organic forms had found little favour in biology “especially on account of the difficult and complicated nomenclature.” But he had complete confidence as to the substance of it, even after so great a lapse of time.

In point of fact we have here, it seems to me, a gigantic preparatory work, not so much for the strict purpose of classification, as for a real philosophy of botany and zoology that will be founded some day. This recurrence of sharp stereometric structures, not only in the crystal, but also, if less clearly, in the biological world, will one day prove an important source of knowledge, in a sense that is not even clear in Haeckel himself.

We are already entering upon a period that has a glimpse of the truth that the deepest power of Beethoven’s music, or Goethe’s poetry, or Raphael’s painting, or Michael Angelo’s sculpture is a mysterious revelation of the most subtle mathematical relations and effects—produced without conscious perception of these relations, though a human mind is at work in them. In spite of all our “consciousness,” the obscure intuitive power at work in these human artistic achievements differs very little from the curious force with which a radiolarian builds up its little house in the deep-sea or a caseworm fits on its fine, rhythmic, snail-like coat. In both we have the same profound, crystal-like constructive power that brought forth the wings of the butterfly, the feathers of the bird, the bodily frame of all the animals and plants, that harmonises so well with strict mathematical forms. In Beethoven and Raphael it is not more conscious or unconscious, not clearer or vaguer, not more mystical or more natural, than in the poorest worm or the microscopically small radiolarian. The æsthetics of the twentieth century will take up these ideas.