It is a great work. How few there are in the whole of the nineteenth century that show the wealth of ideas we find in the first volume alone.^[4] And this is only one volume. We have as yet said nothing of the idea that is of the greatest consequence in connection with Haeckel’s own development. He was a Darwinian from 1862 onwards. After 1866 and the publication of the General Morphology we find him dominated in all his work by one single idea from the Darwinian group. He brought this idea so effectively to the front, improved and developed it so assiduously, and applied it in so many ways, that it has come to be regarded as his own most characteristic work. It is inseparable from his name. Whatever the future may be, wherever Haeckel’s name is uttered people will add the phrase that was made peculiarly his after 1866, that colours and pervades all his works—technical, popular, polemical, or philosophical—as much as the word “Monism.” It is the phrase: the biogenetic law.

Here and there even in the first volume of the Morphology a note is struck that the reader cannot clearly understand. It increases in the second volume until it dominates the whole book.

The phrase is known far and wide to-day. This is partly due to Haeckel’s own insistence on it, but perhaps still more to the real value of the idea itself. It crops up in a hundred different fields—psychology, ethics, philosophy, even in art and æsthetics. I have been able to trace it even into modern mysticism. For the moment I will only point out that it has been attacked and misstated with real fanaticism, in spite of the splendid and perfectly clear account of it that Haeckel has given.

The proper place to read of it is, as I said, the second volume of the Morphology. This volume has to give an account of the evolution of organic forms. What is given rather casually, almost Socratically, in Darwin is now developed into a number of strict laws. This method of expounding more or less hypothetical, new, and insecure ideas in the form of laws has since been frequently attacked. Some have been led by it to take the ideas as so many dogmas, and even to learn the laws by heart as if they were texts in Scripture. Others have then laid the blame of this dogmatic interpretation on Haeckel himself. It is quite true that there was the possibility of a misunderstanding. People do not always think for themselves, and the statement of a proposition in the form of a law may prove a pitfall for them. The blind learning of them by heart is always mischievous. On the other hand, it might be urged that the statement of the ideas in this bald way affords the best opportunity for a thorough and rational criticism of them, precisely because they give such pregnant expression to the writer’s meaning. I do not find that order and strict logical definitions have ever done any harm of themselves, whatever it is that is put in order and defined. On the contrary. People must confuse order sometimes with real dogmatism. Of this there is not a word in the whole book, while at an important juncture the reader is actually warned to be on his guard against undue pressure. “In this,” we read in the twentieth chapter, “we do not wish to draw up a body of laws of organic morphology, but to give hints and suggestions for drawing them up. A science that is yet only in its cradle, like the morphology of organisms, will have many important changes to undergo before it can venture to claim for its general propositions the rank of absolute and unexceptionable natural laws.”

However that may be, it was in this provisional definition of laws that the famous biogenetic law first took shape, and with it a spirit entered into Darwinism in the narrower sense that was never again detached from its master, Haeckel.

Let us once more take a simple illustration from facts. Take a green aquatic frog and a fish, say a pike.

Both of them have a solid vertebral column in their frames, and therefore both must be classed amongst the vertebrates. But within the limits of this group they differ very considerably from each other. The frog has four well-developed legs, its body terminates in a tail, and it breathes by means of lungs, like a bird, a dog, or a human being. The fish has fins, it swims in the water by means of these fins and its long rudder-like tail, and it breathes the air contained in the water by means of gills. When we arrange the vertebrates in a series, with man at their head, it is perfectly clear that the frog stands higher than the fish in regard to its whole structure. It is lower than the lizard, the bird, or the mammal, but at the same time it is a little nearer to these three than the fish is. That was recognised long ago by Linné, who assigned them a corresponding rank. The fishes are the lowest group of the vertebrates; the frogs belong to the group immediately above them. Now let us see how one of these frogs is developed to-day. The frogs are oviparous (egg-laying) animals. The mother frog lays her eggs in the water, and in the ordinary course of nature a new little frog develops from each of these eggs. But the object that develops from them is altogether different from the adult frog.

This object is the familiar tadpole. At first it has no legs, but it has a long oar-like tail, with which it can make its way briskly in the water. It breathes in the water by means of gills just like a fish. It is only when the tadpole grows four legs, loses its tail, closes up the gills at its throat, and begins to breathe by the mouth and lungs instead, that it becomes a real frog. There can be no doubt whatever that the tadpole is very much more like the fish in all the most important particulars than the frog. Between the frog-egg and the frog itself we have a stage of development in each individual case of which we might almost say that the young frog has first to turn into a fish before it can become a frog.

How are we to explain this?

At first people supposed something like the following: All beings in nature are admirably adapted to their environment and their life-conditions. Whatever be the explanation of it, it is a simple fact. Now, the frog lays its eggs in the water. The young ones develop from these eggs, and find themselves in the water. The most practical adaptation for them is to swim about by means of a tail and breathe by means of gills like the fish. They do not reach land until later, and they creep on to it and have an equipment of the opposite character, with legs and lungs.

But this explanation throws no light on the question why the frog lays its eggs in the water. However, there might be some utility or other, some need for protection, for instance, in that. Let us take a few other cases.

There are several species of tree-frogs, and toads, and closely related amphibia like the salamanders, that do not lay their eggs in the water. Some of them bury them in folds of their own external skin, others (such as the Alpine salamander) retain them within the mother’s body, as the mammals do. The young animals develop there from the eggs. Even there, however, where there is no question of aquatic life, the young frogs, toads, and salamanders first assume the fish-form. The young frogs and toads have fin-like tails, and all of them have gills. There seems to be some internal law of development that forces the frog and its relatives to pass through the fish-stage in their individual evolution even when there is no trace whatever of any external utility.

Now let us examine the matter as Darwinians and believers in evolution.

There are reasons on every hand for believing that the frogs and salamanders, which now stand higher in classification than the fishes, were developed from the fishes in earlier ages in the course of progressive evolution. Once upon a time they were fishes. If that is so, the curious phenomenon we have been considering really means that each young frog resembles its fish-ancestors. In each case to-day the frog’s egg first produces the earlier or ancestral stage, the fish. It then develops rapidly into a frog. In other words, the individual development recapitulates an important chapter of the earlier history of the whole race of frogs. Putting this in the form of a law, it runs: each new individual must, in its development, pass rapidly through the form of its parents’ ancestors before it assumes the parent form itself. If a new individual frog is to be developed, and if the ancestors of the whole frog-stem were fishes, the first thing to develop from the frog’s egg will be a fish, and it will only later assume the form of a frog.

That is a simple and pictorial outline of what we mean when we speak of “the biogenetic law.” We need, of course, much more than the one frog-fish fact before we can erect it into a law. But we have only to look round us, and we find similar phenomena as common as pebbles.

Let us bear in mind that evolution proceeded from certain amphibia to the lizards, and from these to the birds and mammals. That is a long journey, but we have no alternative. If the amphibia (such as the frog and the salamander) descend from the fishes, all the higher classes up to man himself must also have done so. Hence the law must have transmitted even to ourselves this ancestral form of the gill-breathing fish.

What a mad idea, many will say; that man should at one time be a tadpole like the frog! And yet—there’s no help in prayer, as Falstaff said—even the human germ or embryo passes through a stage in the womb at which it shows the outline of gills on the throat just like a fish. It is the same with the dog, the horse, the kangaroo, the duck-mole, the bird, the crocodile, the turtle, the lizard; they all have the same structure. Nor is this an isolated fact. From the fish was evolved the amphibian; from this came the lizard; from the lizard, on Darwinian principles, the bird. The lizard has solid teeth in its mouth; the bird has no teeth in its beak. That is to say, it has none to-day; but it had when it was a lizard. Here, then, we have an intermediate stage between the fish and the bird. We must expect that the bird-embryo in the egg will show some trace of it. As a matter of fact it does so. When we examine young parrots in the egg we find that they have teeth in their mouths before the bill is formed. When the fact was first discovered, the real intermediate form between the lizard and the bird was not known. It was afterwards discovered at Solenhofen in a fossil impression from the Jurassic period. This was the archeopteryx, which had feathers like a real bird, and yet had teeth in its mouth like the lizard when it lived on earth. The instance is instructive in two ways. In the first place it shows that we were quite justified in drawing our conclusions as to the past from the bird’s embryonic form, even if the true transitional form between the lizard and the bird were never discovered at all. In the second place, we see in the young bird in the egg the reproduction of two consecutive ancestral stages: one in the fish-gills, the other in the lizard-like teeth. Once the law is admitted, there can be nothing strange in this. If one ancestral stage, that of the fish, is reproduced in the young animal belonging to a higher group, why not several?—why not all of them? No doubt the ancestral series of the higher forms is of enormous length. What an immense number of stages there must have been before the fish! And then we have still the amphibian, the lizard, and the bird or mammal, up to man.

Why should not the law run: the whole ancestral series must be reproduced in the development of each individual organism? We are now in a position to see the whole bearing of Haeckel’s idea, and at the same time to appreciate his careful restrictions of it.

First, let us see a little of the history of the matter. In the first third of the nineteenth century a number of pre-Darwinian ideas of evolution flitted about like ghosts in natural philosophy, as I have already said. The evolutionary ideas of Goethe and Lamarck are well known to-day. Another thinker of great influence was Lorentz Oken, who established the custom of holding scientific congresses. Oken had been constantly occupied with embryology, the science of the development of the individual organism. He was at all events acquainted with all that was known at the time on the subject. I open an old volume, wretchedly printed on blotting-paper, of Oken’s General Natural History for all Readers (1833), and turn to a passage in the fourth volume (the first to be issued) on page 470.

We read that the caterpillar of the butterfly resembles the animal form at a stage of development that lies below the insect—the worm. Oken says: “There is no doubt that we have here a striking resemblance, and one that justifies us in thinking that the development in the ovum is merely a repetition of the story of the creation of the animal groups.” Oken was quite aware that the chick in the egg had gill-slits like the fish. He bases his idea on that fact. He was very close indeed to the theory that Haeckel has so wonderfully elaborated. However, he was greeted with laughter. His theory was treated as an absurdity from 1833 to 1866. It cannot be denied that he was himself partly to blame for this. Oken made two serious mistakes. On both points Haeckel is perfectly clear and sound. Moreover, the theory of natural evolution that made it possible for us to speak of “ancestors” was still a Cinderella in the days of Oken. No sooner was it rehabilitated than the principle of the old theory of embryonic forms returned once more.

Darwin himself at once appealed to it, but it was reserved for Haeckel to develop its full importance. He corrected it in two particulars. Oken and his admirers had made an unfortunate mistake. They believed in a genealogical tree of all living things, but they conceived it on the lines of the old classification. Linné had enumerated in succession: mammals, birds, amphibia, fishes, insects, and worms. He put them in one straight line, which is certainly the best arrangement for general purposes. But when Oken came with the idea of natural evolution, he at once took this series as the outline of a genealogical tree. The mammals descended from the birds; the fishes from the insects; and so on. If that were really the case, the highest animals would be expected to reproduce all the animal and plant stages in the course of their embryonic development, on the lines of the theory. The human being would have to be, successively, not only a lizard and a fish, but even a bird, a beetle, a crab, and so on. This was by no means borne out by the facts, and so the theory seemed to be discredited.

Now let us glance at Haeckel’s genealogical tables. We find eight of them, artistically drawn, at the end of the second volume. The “genealogical tree” is given in the form of a branching tree, or as a huge forest-like growth of stems some of which only meet in the ultimate roots. There is no trace in Haeckel’s designs of the sort of Eiffel-Tower arrangement that the Linnean system involved. At the bottom we find the protists, the most primitive forms of life. From this point two parallel stems diverge, that of the animals and that of the plants; they never touch each other after this point, and so cannot be expected to be reproduced in the embryonic forms. Then the animal stem is split up almost at the root into at least five independent branches, each of which pursues its separate line of development. One culminates in the insects, above the worms and the crustacea. A totally independent stem issues in the vertebrates, and this in turn breaks into many different branches. Beyond the lizards, for instance, we find the development of the mammals and birds, which run on as separate and parallel lines. It was mere nonsense to expect a mammal in its embryonic development to assume the form of a bird, or a crab, or a beetle, or a mussel, or a medusa, even if the biogenetic law were established ten times over.

The second mistake made by Oken was to declare that, whatever it cost, the law must be observed everywhere. He examined the butterfly. It passed through two curious embryonic stages: first the caterpillar, then the pupa. The caterpillar corresponded to the worm; that might be plausibly contended. But the pupa also must stand for something. Between the worm and the insect in classification was the crustacean. It had a hard shell: so had the pupa. Consequently, the pupa is a reproduction of the crustacea-stage. Such were the bold chess-moves of the older theorist.

Haeckel first established that there was such a thing as the biogenetic law. There is a fundamental norm, which is made clear to us in embryology and can at the same time (remember the instance of the lizard-like teeth in the bird-embryo) give us most wonderful suggestions as to the line of ancestral development. But it has certain limitations, as we will now show.

The adaptations in the sense of the Darwinian laws have affected the animal’s embryonic life more and more, the higher the tree of life grew. The long recapitulation of the ancestral stages often came into conflict with the young individual’s need for protection. The result was that the biogenetic law found itself restricted by the Darwinian laws of adaptation. The too lengthy succession of ancestral portraits was abbreviated and compressed. Whole stages of embryonic or larval development were interpolated that had nothing to do with these ancestral portraits, but were destined for the protection of the fœtus. The butterfly-pupa is really an instructive instance of this description. It does not reproduce a crab-stage, nor has there been any stage in the ancestry of the butterfly when they lived throughout life in pupa-houses. The pupa is simply a later adaptation in the development of the butterfly, a protective stage in which it accomplishes the transition from the caterpillar-form in much the same way as the young bird develops under the protection of the hard egg-shell. Thus only a faint and shadowy trace has been left of the real ancestral forms, though this trace is an extremely instructive one. But we must not expect the impossible from it. In this way our naked and crude biogenetic law assumes a more finished and scientific form: the embryonic development of the individual is a condensed, abbreviated, and to some extent modified epitome of the evolutionary history of its ancestors. That is more modest, but it is a correct expression of the facts. The essential point of the older idea was not in itself wrong; all that was done was to explain the gaps, and leaps, and contradictions in it.

Now that Oken’s share in the theory has been properly appreciated, we may notice another little historical detail. In the period immediately after his time these ideas were ridiculed by men of science, great and small, but they were not exactly “done to death.” Agassiz, the most pronounced creationist and dualist of all the nineteenth-century zoologists, expounded them occasionally as a curious instance of the divine action. In fact, he looked upon the whole of zoology as a mystic cabinet of curiosities—the more curious the better. Thus he came to play with this idea and confirm it, but merely took it at first as a fine figure of speech. Agassiz is a tragical form. He survived Darwin, much in the same way that many an elegant mot-de-salon on the rights of man survived the French Revolution. Suddenly the whole structure of his ideas seemed to fall about him. Where he had played with roses, he now found torches. He reeled like a smitten man, and cried out against the horrid monsters that brought him pain and bitterness. His anxiety began with Darwin, even as regarded the question of the embryo. But there was another, a man far away in South America, that increased it—Fritz Müller.

Born in 1822, one of the finest pioneers in zoological work, Fritz Müller had wished to become a higher teacher, but had abandoned his plan on account of the oath that had to be taken by every servant of the State. In 1849 he wrote to the Ministry requesting that he might be allowed to dispense with the formula “So help me God, through Jesus Christ.” Meeting with a refusal, he went to South America, and began a solitary life as a student in the primitive forest, and sought to accumulate valuable zoological material. Darwin called him “the king of observers.” In 1864 he published an essay of ninety-four pages with the title For Darwin. He revived and improved the old idea of Oken’s and made fresh contributions to the natural history of the crustacea that were literally stupefying. We may say that the point that he believed he had established, in virtue of the law, in regard to the genealogical tree of the crustacea, was afterwards, with apparent justice, called into question, even by supporters of the law such as Arnold Lang. That, however, did not diminish the extent of his influence at the time. Haeckel has generously acknowledged how strongly he felt that influence himself. Nevertheless all that has been said about Haeckel’s priority in fully applying and shaping the law, and in its final formulation, is perfectly correct.

When Haeckel had massed his material he had first to create the necessary terms for arranging it distinctly. In the language of the old legend, he called the day day, and the night. To the story of ancestral development, or the evolution of the stem, he gave the name of phylogeny, or stem-history (phylon = stem). The word circulates very widely to-day. The story of the development of the individual until it reaches maturity was then called ontogeny (on = being), which coincides generally with embryology (though it may also include the growth of the child). The law then ran: Ontogeny is an abbreviated and frequently disarranged epitome of phylogeny. Special attention was drawn to the qualifications “abbreviated” and “disarranged.”

Here again two fresh names were invented. In so far as the embryonic development is a true recapitulation of the stem-history, it is called palingenesis, or repetition of the ancestral traits. When the development is altered by new adaptations it is called cenogenesis, “foreign” or “disturbing” development.

It has been objected by small-minded critics that Haeckel forces nature to mar its own work. The real meaning is quite clear if we bear in mind the blunder of Oken. In this case “disturbed development” is merely an expression of the fact that the laws we invent are ideal forms, and not always convenient realities. We learn by heart that the earth is a globe, and its orbit is an ellipse. Neither of the two propositions is strictly accurate; no mathematical figure even has objective reality. By the sheer attraction of the water of the ocean to the continents the earth has an irregularity of shape that it is barely possible to express in words. To call the path of the earth round the sun, constantly altering as it does, and still further complicated by the sun’s own movement, a real ellipse is the greatest nonsense conceivable.

In this sense every natural law is subject to disturbances, though these in turn are the outcome of natural laws. If we do not cavil over the name, we find that the idea it stands for is of the greatest consequence for any further use of the biogenetic law. Unless it is borne in mind, the law, especially in the hands of the inexpert, falls into hopeless confusion. We read so often that the ancestral history is identical with the embryonic development. The one is a recapitulation of the other. This supposed law is then applied in psychology, æsthetics, and many other directions. If it succeeds, there is jubilation. If it does not succeed (as it does not in a thousand cases), the whole blame is thrown on Haeckel. People discover that “the biogenetic law breaks down here,” and they throw over Darwinism altogether.

The second volume of the Morphology is the standing palladium against all this nonsense. It marks off the real readers and followers of Haeckel from the superficial talkers who run after him because he is famous, and will leave him unscrupulously for any other celebrity of the hour.

The book must be read. Even in this second volume an incredible amount of matter is compressed. An introduction, consisting of a hundred and sixty pages of small type, gives us an idea of the new system. This is the first scheme of a real “natural classification” of living things. From this we pass to special morphology. But this fearless sketch of the specialised genealogical tree, according to the new ideas, puts general morphology in its true light. We are made to feel that it is not all mere theory. To-morrow—nay, to-day—the whole practice of zoology and botany will have to be remodelled on the new principles. Off with the roof of the ark! The whole museum must be cleared out. We want new divisions, new labels. The old controversy between the Nominalists and the Realists seemed to have come to life once more. How students had played with the word “affinity” as a symbol. The lemurs were “related” to the apes, and to other groups of mammals. The star-fishes were related to the sea-urchins, to the encrinites. The word had, in fact, led to a certain amount of arrangement; the stuffed or dried or preserved specimens in the museum were placed side by side. Suddenly the whole thing became a reality. The things that were “related” to each other had really been connected historically in earlier ages. The lemurs were the progenitors of the apes. Behind them were a series of other mammals. Star-fishes, sea-urchins, and encrinites, formed a definite branch of the great tree, and were historically connected; not symbolically, but in a real extinct common ancestor.

It was a vast work. A single man had at first the whole kingdom in his hands, had to reject the old lines of demarcation and create new ones. There was a certain advantage at the time. Since Cuvier’s time an immense quantity of new discoveries had accumulated for the construction of a system of living things. Müller, Siebold, Leuckart, Vogt, and many others, had done a great deal of preparatory work. All this was of great assistance to the man who now came forward with courage and a talent for organisation. Nevertheless it needed real genius, together with almost boundless knowledge, to accomplish the task. We must remember how reactionary (even apart from the question of evolution) was the systematic work of distinguished and assuredly learned zoologists like Giebel at that time; they worked on in a humdrum way as if the more advanced students did not exist. How different it has all become since Haeckel’s thorough reform of classification! We are astounded to-day at the skill with which he drew lines in his very first sketch that were so near to the permanent truth. I need only point to the new scheme of the classification of the vertebrates. A good deal of his work was, of course, bound to be defective, because the facts were not yet known; for instance, in fixing the point at which the vertebrates may have evolved from the invertebrates. It was not until a year later that the discovery of the embryonic development of the ascidia by Kowalewsky threw light on this. Again, there was the solution of the problem of the ultimate root-connection of the great parallel animal stems. In this matter Haeckel himself brought illumination by his gastræa-theory.

On the whole this systematic introduction to the second volume would have sufficed of itself to secure for Haeckel a prominent position in the history of zoology and botany. He himself was chiefly proud of the fact that it was the first natural-philosophical system on the new lines to meet the rigorous demands of academic science, and indeed to revolutionise academic science. This enhances his complete triumph in the last two books of the volume. First man is introduced, with absolute clearness and decisiveness, into the system of evolved natural beings, as crown of the animal world, but subject to the same laws as the animal: a vertebrate, a mammal, whose nearest relatives are the anthropoid apes. Thus at last the “system of nature” was complete. It embodied the unity of nature. It formed the framework of facts for a unified natural philosophy, Monism. The monon, the “one,” embracing all things, that included nature in itself and itself in nature, became the last scientific definition of what people called “God.”

Thus the volume, which had begun the system of nature with the monera, closes with a chapter on the Monistic God—“the God in nature.” The conception of God in human fashion is rejected. Man is merely a vertebrate, a mammal, adapted in his whole structure to our little planet. A supreme Being to whom we ascribe omnipresence could not possibly be confined within the narrow limits of this vertebrate and mammal organisation. When we try to do so we fall into unshapely conceptions that are wholly unworthy of the most exalted of all words, ideas, and beings. It is in this connection that Haeckel uses for the first time the phrase “gaseous vertebrate,” that has so often been quoted and attacked since. He means to say that we are driven to such debasing and senseless definitions if we do not recognise in God the essence of the whole system of things; if we form our idea of him arbitrarily on any particular property of things within the system. We must beware—as he expressly says—of such confused and unworthy comparisons.

“Our philosophy,” Haeckel continues, “knows only one God, and this Almighty God dominates the whole of nature without exception. We see his activity in all phenomena without exception. The whole of the inorganic world is subject to him just as much as the organic. If a body falls fifteen feet in the first second in empty space, if three atoms of oxygen unite with one atom of sulphur to form sulphuric acid, if the angle that is formed by the contiguous surfaces of a column of rock-crystal is always 120 degrees, these phenomena are just as truly the direct action of God as the flowering of the plant, the movement of the animal, or the thought of man. We all exist ‘by the grace of God,’ the stone as well as the water, the radiolarian as well as the pine, the gorilla as well as the Emperor of China. No other conception of God except this that sees his spirit and force in all natural phenomena is worthy of his all-enfolding greatness; only when we trace all forces and all movements, all the forms and properties of matter, to God, as the sustainer of all things, do we reach the human idea and reverence for him that really corresponds to his infinite greatness. In him we live, and move, and have our being. Thus does natural philosophy become a theology. The cult of nature passes into that service of God of which Goethe says: ‘Assuredly there is no nobler reverence for God than that springs up in our heart from conversation with nature.’ God is almighty: he is the sole sustainer and cause of all things. In other words, God is the universal law of causality. God is absolutely perfect; he cannot act in any other than a perfectly good manner; he cannot therefore act arbitrarily or freely—God is necessity. God is the sum of all force, and therefore of all matter. Every conception of God that separates him from matter, and opposes to him a sum of forces that are not of a divine nature, leads to amphitheism (or ditheism) and on to polytheism. In showing the unity of the whole of nature, Monism points out that only one God exists, and that this God reveals himself in all the phenomena of nature. In grounding all the phenomena of organic or inorganic nature on the universal law of causality, and exhibiting them as the outcome of ‘efficient causes,’ Monism proves that God is the necessary cause of all things and the law itself. In recognising none but divine forces in nature, in proclaiming all natural laws to be divine, Monism rises to the greatest and most lofty conception of which man, the most perfect of all things, is capable, the conception of the unity of God and nature.”

The book closes with these words and a quotation from Goethe. It had opened with a quotation from Goethe. Goethe runs through the whole of the two energetic volumes like an old and venerable anthem. The stalwart fighter not only traces his whole Monistic philosophy to Goethe: not only owes to him the very idea of morphology. In front of the second and more strictly Darwinistic volume he has a dedication “to the founders of the theory of evolution,” and between Darwin and Lamarck we find the name of Goethe. It was Haeckel’s firm conviction that Goethe not only believed in the unity of God and nature, but literally in the natural evolution of the various species of animals and plants from each other. In this conviction, which claims Goethe explicitly for Darwin, he has never been shaken, although his own friends and convinced evolutionists (Oscar Schmidt, for instance) have often opposed him on the point.

Much has been written since the days of the General Morphology both for and against this Goethe-Darwin theory, but I cannot see that we have got much further with it. I still find that a candid study of some of Goethe’s smaller writings, such as the History of my Botanical Studies, the criticism of D’Alton’s Sloths and Pachyderms (which is very important), and several others, compels us to think that Goethe really believed, in a strikingly Darwinian way, in a slow transformation and evolution of animal and plant species in virtue of purely natural laws; and that he always laid great stress on this idea of his as an original notion, far in advance of the professional science of his time. We not only have several clear passages, but the whole point of his argument really rests on this idea. Hence, apart altogether from the pedantry that tries to make a cabalistic mystery out of Goethe’s works, and always reads B for A and C for B, it does seem that there was truth in Haeckel’s first view of the matter, in spite of all the ink that has been shed over it and the vast amount of word-splitting exegesis. Darwinism has, in a certain sense, its German side, even apart from all that Haeckel has done for it.

This was the book, then, that the deeply afflicted author wrung from himself as his “testament.” It was written and printed with unprecedented speed. When the first copies were issued, the author had a feeling that he had nearly “done for himself.” He could not sleep. The state of his nerves gave great concern to his friends, who were watching him most anxiously. With a stolid fatalism, as if nothing mattered now, he yielded to their pressing advice, and decided to travel for a time. Far away on the blue Atlantic, at the gate to all the glories of the tropics, there is an island, Teneriffe, that was counted one of “the isles of the blest” in the old Roman days. A huge volcano rises from it, and on its flanks we find all the zones of the geography of plants, as in a model collection. Humboldt has given us a splendid description of it, as the first station of his voyage to the tropics. “The man who has some feeling for the beauty of Nature,” he says, “will find a more powerful restorative than climate on this lovely island. No place in the world seems to me better calculated to banish sorrow and restore peace to an embittered soul.” Haeckel went there.

It was not an expensive journey, but it came as a fresh greeting from Nature. It was a new ocean after the long studies on the Mediterranean. What might it not afford in the way of medusæ and other zoological prizes when the general beauty of the landscape, that had enchanted Humboldt, had been fully enjoyed. With a mingling of his overflowing passion for Nature, and the gloomy fatalism that told him this would be his “last voyage” after his “last book,” he asked permission to leave Jena in the autumn of 1866, when the printing of the Morphology was completed, and set out. It was no more to be his last voyage than the Morphology to be his last testament. Although still subdued with resignation in his inner life, he came home in the spring of 1867 with a new elasticity of body and mind, restored by the influence of the palms and bananas and spurge, and braced for the great struggle of his life that was now to begin in earnest.

The voyage had really two aims. To see the volcano above a palm-clad coast, with the Atlantic Ocean bringing its medusæ; and to work for Darwin.

A personal connection between the two had already been formed as a matter of course. Darwin, almost confined for years to his isolated home at Down owing to his constant ill-health, had received a copy of the Radiolaria, and the correspondence had begun. The work had as yet met with little encouragement from the ranks of exact scientists. It cannot have been a matter of indifference to Darwin personally that so distinguished a work, a real model of professional research, had come over to him. Proofs of the Morphology were sent over to Down before the book was ready for publication. Darwin read German with difficulty, but in this case he was stimulated to make an unusual effort. At last Haeckel himself made his appearance at the master’s home. It seemed as though he had to visit him in person to receive his blessing. It was, at all events, a happy moment in the history of Darwinism when the two men first met whose names will be inseparable in literature.

This was in October, 1866; Darwin had sent his carriage to bring Haeckel from the station. A sunny autumn morning smiled on the homely and beautiful English landscape with its bright woods and golden broom and red erica and evergreen oaks. Haeckel has described their first meeting. “When the carriage drew up before Darwin’s house, with its ivy and its shadowy elms, the great scientist stepped out of the shade of the creeper-covered porch to meet me. He had a tall and venerable appearance, with the broad shoulders of an Atlas that bore a world of thought: a Jove-like forehead, as we see in Goethe, with a lofty and broad vault, deeply furrowed by the plough of intellectual work. The tender and friendly eyes were overshadowed by the great roof of the prominent brows. The gentle mouth was framed in a long, silvery white beard. The noble expression of the whole face, the easy and soft voice, the slow and careful pronunciation, the natural and simple tenor of his conversation, took my heart by storm in the first hour that we talked together, just as his great work had taken my intelligence by storm at the first reading. I seemed to have before me a venerable sage of ancient Greece, a Socrates or an Aristotle.”

They were delighted to meet each other, for they were like natures, in their best qualities. Darwin had more passion in him than he ever expressed, and behind all Haeckel’s impetuosity there was the naïve and yielding temper of the child. He poured out his anger against the stubborn and bewigged professors who still held out against the luminous truth of the theory of evolution. Darwin put his hand on his shoulder, smiled, and said they were rather to be pitied than blamed, and that they could not keep back permanently the stream of truth. At heart, however, he was delighted with his fiery pupil. They were to fight their battle shoulder to shoulder for seventeen years. During all those years there was never the slightest disturbance of their friendship. Darwin knew well what an auxiliary he had in Haeckel. It is true that he wrote him a wonderful letter occasionally, in which he used the right of a senior to warn Haeckel not to deal so violently with his opponents. Violence only had the effect of making onlookers side with the party you attacked. We must be careful not to be too hasty in setting things up as positive truths, as we see every day people starting from the same premises and coming to opposite conclusions. But he was generally at one with Haeckel, and had the good spirit to acknowledge it openly. When Haeckel’s History of Creation raised up the most extreme parties, and started the cry that a distinction must be drawn at once between Darwin’s real scientific ideas and Haeckel’s desperate excursions into natural philosophy, Darwin said, in the Descent of Man, which he had begun much earlier, but did not publish for some time, that he would never have written his book if he had then known Haeckel’s History of Creation. Haeckel had anticipated so much that he wished to say. And when Virchow attacked Haeckel in 1877, Darwin spoke very severely of the opponents who would make the eternal freedom to teach the truth dependent on the accidental conditions of a modern State. Haeckel visited him twice at Down. On February 12, 1882, he sent Darwin his congratulations on his seventy-third birthday from the summit of Adam’s Peak in Ceylon. This was his last greeting. Darwin died two months afterwards. There was a touch of romance in this last communication of the two great warriors. On the summit of the mountain, almost as sharp as a needle, and 2,500 yards above the Indian Ocean, a tiny temple of Buddha hangs like a stork’s nest suspended by chains. Buddha is believed to have left his footprints on the rocks here. The Mohammedan tradition, however, says it was done by Adam as he stood on one foot and bemoaned the loss of Paradise. In front of this holy trace, a depression in the rock about a foot long, Haeckel made a speech to his travelling companions, and they broke the neck of a bottle of Rhine wine to Darwin’s health. It is no little stretch of humanity’s pilgrimage, from Adam to Buddha and on to Darwin.

In October, 1866, Haeckel had a companion in a teacher from Bonn, Richard Greeff (afterwards professor of zoology at Marburg). They took ship from London to Lisbon, where they were long detained for quarantine, though the annoyance was somewhat relieved by the discovery of an interesting medusa in the brackish water of the Tagus. They then went to Madeira and Teneriffe, not right into the tropics, but where they might get a breath of it, as it were. Two of Haeckel’s pupils, who both became well known afterwards, Miklucho-Maclay and Fol, were with them. Greeff has given a full account of the journey in a whole volume (published at Bonn, 1868), and Haeckel has written of it in two articles, one of which (in the fifth volume of the Zeitschrift der Gesellschaft für Erdkunde, Berlin, 1870) is a perfect masterpiece of narrative and description of scenery. After a long search they chose as the best station for studying marine animals, especially the medusæ, the little island of Lanzarote, instead of one of the chief islands. Here they fished and drew, in the manner taught by Johannes Müller, for three months, from December, 1866, to February, 1867. It is not exactly an ideal place. “Imagine yourself dumped down on the moor!” Haeckel said afterwards in his description of it. A piece of arid land that looked like a strip of the Sahara in the middle of the ocean. There is hardly any water, and the vegetation is correspondingly meagre. Across the middle of the island stretches a chain of volcanic craters, and old lava-fields run down from them as far as the coast. Everything of zoological interest in the place was to be found in the sea. There they found abundance. As in Messina, certain local currents drove the rich animal plancton together until there were literally rivers or streets of tiny animals. One had only to dip in one’s nets and glasses, and bring up whole shoals with every drop of water.

Haeckel had come chiefly to study the medusæ. But this led him on much further to a great zoological problem. In his General Morphology he had expounded his brilliant ideas on the subject of individuality, and now he encountered in the flesh one of the greatest marvels of animal individuality. He had shown how the higher individual is always made up of a community, a kind of state, of lower individuals. In the simplest instance there are the cells. Each of them is an individual. Millions of these individuals, banded together with division of labour for great collective operations, make up the human frame, and therefore the human “individual.” In the same way others form a beetle, a snail, or a single medusa. Sometimes, however, these higher individuals enter in turn into social combinations to form still higher communities. Human beings form social commonwealths, with division of labour among the individuals. Bees and ants form their communities in the same way. But in the latter cases the texture of the community seems to be much looser than in the preceding one. It is not so easy for the imagination to grasp a human commonwealth or a colony of bees as a real “over-individual.” It is, therefore, extremely instructive to find that at least one animal community of this kind is of so firm a texture that even on the most superficial examination it is recognised at once as an individual. This is found in one of the groups of the medusæ, the siphonophores, or social medusæ.

A number of single medusæ, each of which corresponds to what we regard as the individual man, combine and form a new body, a social individual. As citizens of this new state they have introduced the most rigid division of labour. One medusa does nothing but eat, and it thus provides nourishment for the rest, as they are all joined in one body. Another accomplishes the swimming movement; another has been converted entirely into a reproductive organ. In a word, the whole has become a “unity” once more, equipped with its various organs like any large body. Sometimes thousands of separate medusæ enter into the structure of one of these wonders of the deep. And as each of the medusæ is generally a very pretty, flower-like creature, the social groups with their charming colours look like floating garlands of flowers made of transparent and tinted crystal. Their beauty would soon fix Haeckel’s attention, but their bearing on his theory of individuality would give them an even greater value. For several years he had searched most attentively in the animal world for these “over-individuals” of the highest class. In the morphology he had had to be content with an old illustration of something of the kind, the star-fish. It was supposed to be a combination of vermalians. In this case the hypothesis has broken down, though there was a good deal to be said for it at first, and it was abandoned by him afterwards. But now, when he saw enormous numbers of siphonophores in the animal streams at Lanzarote, he entered upon a decisive study of the meaning of these real “social animals.” A social medusa has so great an appearance of unity that those who discovered it first did not believe it was a community, but a very complicated individual medusa. Vogt (1847) and Leuckart (1851) had denied this, and declared it to be a social group. But the controversy was still going on, as there was much difference of opinion as to the meaning of “social” and “state.” Haeckel now succeeded at Lanzarote in tracing for the first time the development of one of these siphonophores from the ovum. He was able to show that from the ovum only a single simple medusa is developed. This, then, becomes the parent of the community; it produces the rest of the members, not by a new sexual generation, but by budding out from itself, until the whole garland of connected individuals is ready to constitute the new over-individual, or the community. These luminous investigations were published three years afterwards (1869) in a work that was crowned by the Utrecht Society of Art and Science (The Embryology of the Siphonophoræ, with fourteen plates, published at Utrecht). But Haeckel returned time after time in later years to this group of animals with such great philosophic and zoological interest. When he had put before him in the eighties the whole of the siphonophores brought home by the splendid Challenger expedition, he combined the material with the results of his own studies in a fine work, which was included (in English) in the publications of the Challenger series at London, as the 28th volume of the Zoology of the Challenger, 1888. The voluminous work is illustrated with fifty masterly plates, some of them coloured, by Haeckel himself. The most important part of the text was also published in German at Jena, with the title, System of the Siphonophoræ. There is a good popular account of the siphonophore question in his lecture on “The Division of Labour in Nature and in Human Life” (1869). A few of these beautiful forms are also given on coloured plates in his illustrated work, Art-forms in Nature. Every thoughtful man ought, whatever his position is as regards Haeckel’s ideas, to glance at this material that he has so vigorously and clearly presented.

While he was conducting this research into the embryonic development of the siphonophores, Haeckel made certain experiments on phenomena that have lately been made the subject of a special “experimental mechanical embryology” by some of his pupils, particularly Professor Roux, of Halle. He cut up siphonophore ova into several pieces at the commencement of their development, and saw an incomplete social medusa develop from each fragment.