PEDIGREE AND HISTORY OF THE KINGDOM OF THE PROTISTA.
Special Mode of Carrying out the Theory of Descent in the Natural System of Organisms.—Construction of Pedigrees.—Descent of all Many-Celled from Single-Celled Organisms.—Descent of Cells from Monera.—Meaning of Organic Tribes, or Phyla.—Number of the Tribes in the Animal and Vegetable Kingdoms.—The Monophyletic Hypothesis of Descent, or the Hypothesis of one Common Progenitor, and the Polyphyletic Hypothesis of Descent, or the Hypothesis of Many Progenitors.—The Kingdom of Protista, or Primæval Beings.—Eight Classes of the Protista Kingdom.—Monera, Amœbæ, or Protoplastæ.—Whip-swimmers, or Flagellata.—Ciliated-balls, or Catallacta.—Labyrinth-streamers, or Labyrinthuleæ.—Flint-cells, or Diatomeæ.—Mucous-moulds, or Myxomycetes.—Root-footers (Rhizopoda).—Remarks on the General Natural History of the Protista: Their Vital Phenomena, Chemical Composition, and Formation (Individuality and Fundamental Form).—Phylogeny of the Protista Kingdom
By a careful comparison of the individual and the palæontological development, as also by the comparative anatomy of organisms, by the comparative examination of their fully developed structural characteristics, we arrive at the knowledge of the degrees of their different structural relationships. By this, however, we at the same time obtain an insight into their true blood relationship, which, according to the Theory of Descent, is the real reason of the structural relationship. Hence by collecting, comparing, and employing the empirical results of embryology, palæontology, and anatomy for supplementing each other, we arrive at an approximate knowledge of “the Natural System,” which, according to our views, is the pedigree of organisms. It is true that our human knowledge, in all things fragmentary, is especially so in this case, on account of the extreme incompleteness and defectiveness of the records of creation. However, we must not allow this to discourage us, or to deter us from undertaking this highest problem of biology. Let us rather see how far it may even now be possible, in spite of the imperfect state of our embryological, palæontological, and anatomical knowledge, to establish a probable scheme of the genealogical relationships of organisms.
Darwin in his book gives us no answer to these special questions of the Theory of Descent; at the conclusion he only expresses his conjecture “that animals have descended from at most only four or five progenitors, and plants from an equal or less number.” But as these few aboriginal forms still show traces of relationship, and as the animal and vegetable kingdoms are connected by intermediate transitional forms, he arrives afterwards at the opinion “that probably all the organic beings which have ever lived on the earth have descended from some one primordial form, into which life was first breathed by the Creator.” Like Darwin, all other adherents of the Theory of Descent have only treated it in a general way, and not made the attempt to carry it out specially, and to treat the “Natural System” actually as the pedigree of organisms. If, therefore, we venture upon this difficult undertaking, we must take up independent ground.
Four years ago I set up a number of hypothetical genealogies for the larger groups of organisms in the systematic introduction to my General History of Development (Gen. Morph. vol. ii.), and thereby, in fact, made the first attempt actually to construct the pedigrees of organisms in the manner required by the theory of development. I was quite conscious of the extreme difficulty of the task, and as I undertook it in spite of all discouraging obstacles, I claim no more than the merit of having made the first attempt and given a stimulus for other and better attempts. Probably most zoologists and botanists were but little satisfied with this beginning, and least so in reference to the special domain in which each one is specially at work. However, it is certainly in this case much easier to blame than to produce something better, and what best proves the immense difficulty of this infinitely complicated task is the fact that no naturalist has as yet supplied the place of my pedigrees by better ones. But, like all other scientific hypotheses which serve to explain facts, my genealogical hypotheses may claim to be taken into consideration until they are replaced by better ones.
I hope that this replacement will very soon take place; and I wish for nothing more than that my first attempt may induce very many naturalists to establish more accurate pedigrees for the individual groups, at least in the special domain of the animal and vegetable kingdom which happens to be well known to one or other of them. By numerous attempts of this kind our genealogical knowledge, in the course of time, will slowly advance and approach more towards perfection, although it can with certainty be foreseen that we shall never arrive at a complete pedigree. We lack, and shall ever lack, the indispensable palæontological foundations. The most ancient records will ever remain sealed to us, for reasons which have been previously mentioned. The most ancient organisms which arose by spontaneous generation—the original parents of all subsequent organisms—must necessarily be supposed to have been Monera—simple, soft, albuminous lumps, without structure, without any definite forms, and entirely without any hard and formed parts. They and their next offspring were consequently not in any way capable of being preserved in a petrified condition. But we also lack, for reasons discussed in detail in the preceding chapter, by far the greater portion of the innumerable palæontological documents, which are really requisite for a safe reconstruction of the history of animal tribes, or phylogeny, and for the true knowledge of the pedigree of organisms. If we, therefore, in spite of this, venture to undertake their hypothetical construction, we must chiefly depend for guidance on the two other series of records which most essentially supplement the palæontological archives. These are ontogeny and comparative anatomy.
If thoughtfully and carefully we consult these most valuable records, we at once perceive what is exceedingly significant, namely, that by far the greater number of organisms, especially all higher animals and plants, are composed of a great number of cells, and that they originate out of an egg, and that this egg, in animals as well as in plants, is a single, perfectly simple cell—a little lump of albuminous constitution, in which another albuminous corpuscle, the cell-kernel, is enclosed. This cell containing its kernel grows and becomes enlarged. By division it forms an accumulation of cells, and out of these, by division of labour (as has previously been described), there arise the numberless different forms which are presented to us in the fully developed animal and vegetable species. This immensely important process—which we may follow step by step, with our own eyes, any day in the embryological development of any animal or vegetable individual, and which as a rule is by no means considered with the reverence it deserves—informs us more surely and completely than all petrifactions could do as to the original palæontological development of all many-celled organisms, that is, of all higher animals and plants. For as ontogeny, or the embryological development of every single individual, is essentially only a recapitulation of phylogeny, or the palæontological development of its chain of ancestors, we may at once, with full assurance, draw the simple and important conclusion, that all many-celled animals and plants were originally derived from single-celled organisms. The primæval ancestors of man, as well as of all other animals, and of all plants composed of many cells, were simple cells living isolated. This invaluable secret of the organic pedigree is revealed to us with infallible certainty by the egg of animals, and by the true egg-cell of plants. When the opponents of the Theory of Descent assert it to be miraculous and inconceivable that an exceedingly complicated many-celled organism could, in the course of time, have proceeded from a simple single-celled organism, we at once reply that we may see this incredible miracle at any moment, and follow it with our own eyes. For the embryology of animals and plants visibly presents to our eyes in the shortest space of time the same process as that which has taken place in the origin of the whole tribe during the course of enormous periods of time.
Upon the ground of embryological records, therefore, we can with full assurance maintain that all many-celled, as well as single-celled, organisms are originally descended from simple cells; connected with this, of course, is the conclusion that the most ancient root of the animal and vegetable kingdom was common to both. For the different primæval “original cells” out of which the few different main groups or tribes have developed, only acquired their differences after a time, and were descended from a common “primæval cell.” But where did those few “original cells,” or the one primæval cell, come from? For the answer to this fundamental genealogical question we must return to the theory of plastids and the hypothesis of spontaneous generation which we have already discussed (vol. i. p. [327]).
As was then shown, we cannot imagine cells to have arisen by spontaneous generation, but only Monera, those primæval creatures of the simplest kind conceivable, like the still living Protamœbæ), Protomyxæ, etc. (vol. i. p. 1[186], Fig. 1). Only such corpuscules of mucus without component parts—whose whole albuminous body is as homogeneous in itself as an inorganic crystal, but which nevertheless fulfills the two organic fundamental functions of nutrition and propagation—could have directly arisen out of inorganic matter by autogeny at the beginning (we may suppose) of the Laurentian period. While some Monera remained at the original simple stage of formation, others gradually developed into cells by the inner kernel of the albuminous mass becoming separated from the external cell-substance. In others, by differentiation of the outermost layer of the cell-substance, an external covering (membrane, or skin) was formed round simple cytods (without kernel), as well as round naked cells (containing a kernel). By these two processes of separation in the simple primæval mucus of the Moneron body, by the formation of a kernel in the interior and a covering on the outer surface of the mass of plasma, there arose out of the original most simple cytods, or Monera, those four different species of plastids, or individuals, of the first order, from which, by differentiation and combination, all other organisms could afterwards develop themselves. (Compare vol. i. p. [347].)
The question now forces itself upon us, Are all organic cytods and cells, and consequently also those “original cells” which we previously considered to be the primary parents of the few great main groups of the animal and vegetable kingdoms, descended from a single original form of Moneron, or were there several different organic primary forms, each traceable to a peculiar independent species of Moneron which originated by spontaneous generation? In other words, Is the whole organic world of a common origin, or does it owe its origin to several acts of spontaneous generation? This fundamental question of genealogy seems at first sight to be of exceeding importance. But on a more accurate examination, we shall soon see that this is not the case, and that it is in reality a matter of very subordinate importance.
Let us now pass on to examine and clearly limit our conception of an organic tribe. By tribe, or phylum, we understand all those organisms of whose blood relationship and descent from a common primary form there can be no doubt, or whose relationship, at least, is most probable from anatomical reasons, as well as from reasons founded on historical development. Our tribes, or phyla, according to this idea, essentially coincide with those few “great classes,” or “main classes,” of which Darwin also thinks that each contains only organisms related by blood, and of which, both in the animal and in the vegetable kingdoms, he only assumes either four or five. In the animal kingdom these tribes would essentially coincide with those four, five, or six main divisions which zoologists, since Bär and Cuvier, have distinguished as “main forms, general plans, branches, or sub-kingdoms” of the animal kingdom. (Compare vol. i. p. [53.]) Bär and Cuvier distinguished only four of them, namely:—1. The vertebrate animals (Vertebrata); 2. The articulated animals (Articulata); 3. The molluscous animals (Mollusca); and 4. The radiated animals (Radiata). At present six are generally distinguished, since the tribe of the articulated animals is divided into two tribes, those possessing articulated feet (Arthropoda), and the worms (Vermes); and in like manner the tribe of radiated animals is subdivided into the two tribes of the star animals (Echinodermata) and the animal-plants (Zoophyta). Within each of these six tribes, all the included animals, in spite of great variety in external form and inner structure, nevertheless possess such numerous and important characteristics in common, that there can be no doubt of their blood relationship. The same applies also to the six great main classes which modern botany distinguishes in the vegetable kingdom, namely:—1. Flowering plants (Phanerogamia); 2. Ferns (Filicinæ); 3. Mosses (Muscinæ); 4. Lichens (Lichenes); 5. Fungi (Fungi); and 6. Water-weeds (Algæ). The last three groups, again, show such close relations to one another, that by the name of “Thallus plants” they may be contrasted with the three first main classes, and consequently the number of phyla, or main groups, of the vegetable kingdom may be reduced to the number of four. Mosses and ferns may likewise be comprised as “Prothallus plants” (Prothallophyta), and thereby the number of plant tribes reduced to three—Flowering plants, Prothallus plants, and Thallus plants.
Very important facts in the anatomy and the history of development, both in the animal and vegetable kingdoms, support the supposition that even these few main classes or tribes are connected at their roots, that is, that the lowest and most ancient primary forms of all three are related by blood to one another. Nay, by a further examination we are obliged to go still a step further, and to agree with Darwin’s supposition, that even the two pedigrees of the animal and vegetable kingdom are connected at their lowest roots, and that the lowest and most ancient animals and plants are derived from a single common primary creature. According to our view, this common primæval organism can have been nothing but a Moneron which took its origin by spontaneous generation.
In the mean time we shall at all events be acting cautiously if we avoid this last step, and assume true blood relationship only within each tribe, or phylum, where it has been undeniably and surely established by facts in comparative anatomy, ontogeny, and phylogeny. But we may here point to the fact that two different fundamental forms of genealogical hypothesis are possible, and that all the different investigations of the Theory of Descent in relation to the origin of organic groups of forms will, in future, tend more and more in one or the other of these directions. The unitary, or monophyletic, hypothesis of descent will endeavour to trace the first origin of all individual groups of organisms, as well as their totality, to a single common species of Moneron which originated by spontaneous generation (vol. i. p. [343]). The multiple, or polyphyletic, hypothesis of descent, on the other hand, will assume that several different species of Monera have arisen by spontaneous generation, and that these gave rise to several different main classes (tribes, or phyla) (vol. i. p. [348]). The apparently great contrast between these two hypotheses is in reality of very little importance. For both the monophyletic and the polyphyletic hypothesis of descent must necessarily go back to the Monera as the most ancient root of the one or of the many organic tribes. But as the whole body of a Moneron consists only of a simple, formless mass, without component particles, made up of a single albuminous combination of carbon, it follows that the differences of the different Monera can only be of a chemical nature, and can only consist in a different atomic composition of that mucous albuminous combination. But these subtle and complicated differences of mixture of the infinitely manifold combinations of albumen are not appreciable by the rude and imperfect means of human observation and are, consequently, at present of no further interest to the task we have in hand.
The question of the monophyletic or polyphyletic origin will constantly recur within each individual tribe, where the origin of a smaller or of a larger group is discussed. In the vegetable kingdom, for example, some botanists will be inclined to derive all flowering plants from a single form of fern, while others will prefer the idea that several different groups of Phanerogama have sprung from several different groups of ferns. In like manner, in the animal kingdom, some zoologists will be more in favour of the supposition that all placental animals are derived from a single pouched animal; others will be more in favour of the opposite supposition, that several different groups of placental animals have proceeded from several different pouched animals. In regard to the human race itself, some will prefer to derive it from a single form of ape, while others will be more inclined to the idea that several different races of men have arisen, independently of one another, out of several different species of ape. Without here expressing our opinion in favour of either the one or the other conception, we must, nevertheless, remark that in general the monophyletic hypothesis of descent deserves to be preferred to the polyphyletic hypothesis of descent. In accordance with the chorological proposition of a single “centre of creation” or of a single primæval home for most species (which has already been discussed), we may be permitted to assume that the original form of every larger or smaller natural group only originated once in the course of time, and only in one part of the earth. We may safely assume this simple original root, that is, the monophyletic origin, in the case of all the more highly developed groups of the animal and vegetable kingdoms. (Compare vol. i. p. [353.]) But it is very possible that the more complete Theory of Descent of the future will involve the polyphyletic origin of very many of the low and imperfect groups of the two organic kingdoms.
For these reasons I consider it best, in the mean time, to adopt the monophyletic hypothesis of descent both for the animal and for the vegetable kingdom. Accordingly, the above-mentioned six tribes, or phyla, of the animal kingdom must be connected at their lowest root, and likewise the three or six main classes, or phyla, of the vegetable kingdom must be traced to a common and most ancient original form. How the connection of these tribes is to be conceived I shall explain in the succeeding chapters. But before proceeding to this, we must occupy ourselves with a very remarkable group of organisms, which cannot without artificial constraint be assigned either to the pedigree of the vegetable or to that of the animal kingdom. These interesting and important organisms are the primary creatures, or Protista.
All organisms which we comprise under the name of Protista show in their external form, in their inner structure, and in all their vital phenomena, such a remarkable mixture of animal and vegetable properties, that they cannot with perfect justice be assigned either to the animal or to the vegetable kingdom; and for more than twenty years an endless and fruitless dispute has been carried on as to whether they are to be assigned to this or that kingdom. Most of Protista are so small that they can scarcely, if at all, be perceived with the naked eye. Hence the majority of them have only become known during the last fifty years, since by the help of the improved and general use of the microscope these minute organisms have been more frequently observed and more accurately examined. However, no sooner were they better known than endless disputes arose about their real nature and their position in the natural system of organisms. Many of these doubtful primary creatures botanists defined as animals, and zoologists as plants; neither of the two would own them. Others, again, were declared by botanists to be plants, and by zoologists to be animals; each claimed them. These contradictions are not altogether caused by our imperfect knowledge of the Protista, but in reality by their true nature. Indeed, most Protista present such a confused mixture of several animal and vegetable characteristics, that each investigator may arbitrarily assign them either to the animal or vegetable kingdom. Accordingly as he defines these two kingdoms, and as he looks upon this or that characteristic as determining the animal or vegetable nature, he will assign the individual classes of Protista in one case to the animal and in another to the vegetable kingdom. But this systematic difficulty has become an inextricable knot by the fact that all more recent investigations on the lowest organisms have completely effaced, or at least destroyed, the sharp boundary between the animal and vegetable kingdom which had hitherto existed, and to such a degree that its restoration is possible only by means of a completely artificial definition of the two kingdoms. But this definition could not be made so as to apply to many of the Protista.
For this and other reasons it is, in the mean time, best to exclude the doubtful beings from the animal as well as from the vegetable kingdom, and to comprise them in a third organic kingdom standing midway between the two others. This intermediate kingdom I have established as the Kingdom of the Primary Creatures (Protista), when discussing general anatomy in the first volume of my General Morphology, pp. 191-238. In my Monograph of the Monera,[(15)] I have recently treated of this kingdom, having somewhat changed its limits, and given it a more accurate definition. Of independent classes of the kingdom Protista, we may at present distinguish the following:—
1. The still living Monera; 2. The Amœboidea, or Protoplasts; 3. The Whip-swimmers, or Flagellata; 4. The Flimmer-balls, or Catallacta; 5. The Tram-weavers, or Labyrinthuleæ; 6. The Flint-cells, or Diatomeæ; 7. The Slime-moulds, or Myxomycetes; 8. The Ray-streamers, or Rhizopoda.
The most important groups at present distinguishable in these eight classes of Protista are named in the systematic table on p. [51.] Probably the number of these Protista will be considerably increased in future days by the progressive investigations of the ontogeny of the simplest forms of life, which have only lately been carried on with any great zeal. With most of the classes named we have become intimately acquainted only during the last ten years. The exceedingly interesting Monera and Labyrinthuleæ, as also the Catallacta, were indeed discovered only a few years ago. It is probable also that very numerous groups of Protista have died out in earlier periods, without having left any fossil remains, owing to the very soft nature of their bodies. We might add to the Protista from the still living lowest groups of organisms—the Fungi; and in so doing should make a very large addition to its domain. Provisionally we shall leave them among plants, though many naturalists have separated them altogether from the vegetable kingdom.
The pedigree of the kingdom Protista is still enveloped in the greatest obscurity. The peculiar combination of animal and vegetable properties, the indifferent and uncertain character of their relations of forms and vital phenomena, together with a number of several very peculiar features which separate most of the subordinate classes sharply from the others, at present baffle every attempt distinctly to make out their blood relationships with one another, or with the lowest animals on the one hand, and with the lowest plants on the other hand. It is not improbable that the classes specified, and many other unknown classes of Protista, represent quite independent organic tribes, or phyla, each of which has independently developed from one, perhaps from various, Monera which have arisen by spontaneous generation. If we do not agree to this polyphyletic hypothesis of descent, and prefer the monophyletic hypothesis of the blood relationship of all organisms, we shall have to look upon the different classes of Protista as the lower small offshoots of the root, springing from the same simple Monera root, out of which arose the two mighty and many-branched pedigrees of the animal kingdom on the one hand, and of the vegetable kingdom on the other. (Compare pp. [74], [75].) Before I enter into this difficult question more accurately, it will be appropriate to premise something further as to the contents of the classes of Protista given on the next page, and their general natural history.
| SYSTEMATIC SURVEY | ||||||
| Of the Larger and Smaller Groups of the Kingdom Protista | ||||||
| Classes of the Protista Kingdom. | Systematic Name of the Classes | Orders of Families of the Classes. | A name of a Genus as an example. | |||
| 1. Moners | Monera |
| 1. Gymnomonera | Protogenes | ||
| 2. Lepomonera | Protomyxa | |||||
| 2. Protoplasts | Amœboida |
| 1. Gymnamœbæ | Amœba | ||
| 2. Leptamœbæ | Arcella | |||||
| 3. Gregarinæ | Monocystis | |||||
| 3. Whip-swimmers |
| Flagellata |
| 1. Nudiflagellata | Euglena | |
| 2. Cilioflagellata | Peridinium | |||||
| 4. Flimmer-balls | Catallacta | 1. Catallacta | Magosphæra | |||
| 5. Tram-weavers | Labyrinthuleæ | 1. Labyrinthuleæ | Labyrinthula | |||
| 6. Flint-cells | Diatomea |
| 1. Striata | Navicula | ||
| 2. Vittata | Tabellaria | |||||
| 3. Areolata | Coscinodiscus | |||||
| 7. Slime-moulds | Myxomycetes |
| 1. Physareæ | Æthalium | ||
| 2. Stemoniteæ | Stemonitis | |||||
| 3. Trichiaceæ | Arcyria | |||||
| 4. Lycogaleæ | Reticularia | |||||
| 8. Ray-streamers or Rhizopods. (Root-feet) |
| I. Acyttaria |
| 1. Monothalamia | Gromia | |
| 2. Polythalamia | Nummulina | |||||
| II. Heliozoa | 1. Heliozoa | Actinosphærium | ||||
| III. Radiolaria |
| 1. Monocyttaria | Cyrtidosphæra | |||
| 2. Polycyttaria | Collosphæra | |||||
Fig. 8.—Protamœba primitiva, a fresh-water Moneron, much enlarged. A. The entire Moneron with its form-changing processes. B. It begins to divide itself into two halves. C. The division of the two halves is completed, and each now represents an independent individual.
It will perhaps seem strange that I should here again begin with the remarkable Monera as the first class of the Protista kingdom, as I of course look upon them as the most ancient primary forms of all organisms without exception. Still, what are we otherwise to do with the still living Monera? We know nothing of their palæontological origin, we know nothing of any of their relations to lower animals or plants, and we know nothing of their possible capability of developing into higher organisms. The simple and homogeneous little lump of slime or mucus which constitutes their entire body (Fig. [8]) is the most ancient and original form of animal as well as of vegetable plastids. Hence it would evidently be just as arbitrary and unreasonable to assign them to the animal as it would be to assign them to the vegetable kingdom. In any case we shall for the present be acting more cautiously and critically if we comprise the still living Monera—whose number and distribution is probably very great—as a special and independent class, contrasting them with the other classes of the kingdom Protista, as well as with the animal kingdom. Morphologically considered, the Monera—on account of the perfect homogeneity of the albuminous substance of their bodies, on account of their utter want of heterogeneous particles—are more closely connected with anorgana than with organisms, and evidently form the transition between the inorganic and organic world of bodies, as is necessitated by the hypothesis of spontaneous generation. I have described and given illustrations of the forms and vital phenomena of the still living Monera (Protamœba, Protogenes, Protomyxa, etc.) in my Monograph of the Monera,[(15)] and have briefly mentioned the most important facts in the eighth chapter (vol. i. pp. [183]-187). Therefore, only by way of a specimen, I here repeat the drawing of the fresh-water Protamœba (Fig. 8). The history of the life of an orange-red Protomyxa adrantiaca, which I observed at Lanzerote, one of the Canary Islands, is given in Plate [I]. (see its explanation in the Appendix). Besides this, I here add a drawing of the form of Bathybius, that remarkable Moneron discovered by Huxley, which lives in the greatest depths of the sea in the shape of naked lumps of protoplasm and reticular mucus (vol. i. p. [344]).
The Amœbæ of the present day, and the organisms most closely connected with them, Arcellidæ and Gregarinæ, which we here unite as a second class of Protista under the name of Amœboidea (Protoplasta), present no fewer genealogical difficulties than the Monera. These primary creatures are at present usually placed in the animal kingdom without its in reality being understood why. For simple naked cells—that is, shell-less plastids with a kernel—occur as well among real plants as real animals. The generative cells, for example, in many Algæ (spores and eggs) exist for a longer or shorter time in water in the form of naked cells with a kernel, which cannot be distinguished at all from the naked eggs of many animals (for example, those of the Siphonophorous Medusæ). (Compare the figure of a naked egg of a bladder-wrack in Chapter xvii. p. [90].) In reality every naked simple cell, whether it proceeds from an animal or vegetable body, cannot be distinguished from an independent Amœba. For an Amœba is nothing but a simple primary cell, a naked little lump of cell-matter, or plasma, containing a kernel. The contractility of this plasma, which the free Amœba shows in stretching out and drawing in its changing processes, is a general vital property of the organic plasma of all animal as well as of all vegetable plastids. When a freely moving Amœba, which perpetually changes its form, passes into a state of rest, it draws itself together into the form of a globule, and surrounds itself with a secreted membrane. It can then be as little distinguished from an animal egg as from a simple globular vegetable cell (Fig. 10 A).
Fig. 10.—Amœba sphærococcus, greatly magnified. A fresh-water Amœba without a contractile vacuole. A. The enclosed Amœba in the state of a globular lump of plasma (c) enclosing a kernel and a kernel-speck (a). The simple cell is surrounded by a cyst, or cell membrane (d). B. The free Amœba, which has burst and left the cyst, or cell-membrane. C. It begins to divide by its kernel parting into two kernels, and the cell-substance between the two contracting. D. The division is completed, and the cell-substance has entirely separated into two bodies. (Da and Db)
Naked cells, with kernels, like those represented in Fig. 10 B, which are continuously changing, stretching out and drawing in formless, finger-like processes, and which are on this account called amœboid, are found frequently and widely dispersed in fresh water and in the sea; nay, are even found creeping on land. They take their food in the same way as was previously described in the case of the Protamœba (vol. i. p. [186]). Their propagation by division can sometimes be observed. (Fig. 10 C, D.) I have described the processes in an earlier chapter (vol. i. p. [187]). Many of these formless Amœbæ have lately been recognized as the early stages of development of other Protista (especially the Myxomycetæ), or as the freed cells of lower animals and plants. The colourless blood-cells of animals, for example, those of human blood, cannot be distinguished from Amœbæ. They, like the latter, can receive solid corpuscles into their interior, as I was the first to show by feeding them with finely divided colouring matters (Gen. Morph. i. 271). However, other Amœbæ (like the one given in Fig. 10) seem to be independent “good species,” since they propagate themselves unchanged throughout many generations. Besides the real, or naked, Amœbæ (Gymnamœbæ), we also find widely diffused in fresh water case-bearing Amœbæ (Lepamœbæ), whose naked plasma body is partially protected by a more or less solid shell (Arcella), sometimes even by a case (Difflugia) composed of small stones. Lastly, we frequently find in the body of many lower animals parasitic Amœbæ (Gregarinæ), which, adapting themselves to a parasitic life, have surrounded their plasma-body with a delicate closed membrane.
The simple naked Amœbæ are, next to the Monera, the most important of all organisms to the whole science of biology, and especially to general genealogy. For it is evident that the Amœbæ originally arose out of simple Monera (Protamœbæ), by the important process of segregation taking place in their homogeneous viscid body—the differentiation of an inner kernel from the surrounding plasma. By this means the great progress from a simple cytod (without kernel) into a real cell (with kernel) was accomplished (compare Fig. 8 A and Fig. 10 B). As some of these cells at an early stage encased themselves by secreting a hardened membrane, they formed the first vegetable cells, while others, remaining naked, developed into the first aggregates of animal cells. The presence or absence of an encircling hard membrane forms the most important, although by no means the entire, difference of form between animal and vegetable cells. As vegetable cells even at an early stage enclose themselves within their hard, thick, and solid cellular shell, like that of the Amœbæ in a state of rest (Fig. 10 A), they remain more independent and less accessible to the influences of the outer world than are the soft animal cells, which are in most cases naked, or merely covered by a thin pliable membrane. But in consequence of this the vegetable cells cannot combine, as do the animal cells, for the construction of higher and composite fibrous tracts, for example, the nervous and muscular tissues. It is probable that, in the case of the most ancient single-celled organisms, there must have developed at an early stage the very important difference in the animal and vegetable mode of receiving food. The most ancient single-celled animals, being naked cells, could admit solid particles into the interior of their soft bodies, as do the Amœbæ (Fig. 10 B) and the colourless blood-cells; whereas the most ancient single-celled plants encased by their membranes were no longer able to do this, and could admit through it only fluid nutrition (by means of diffusion).
Fig. 11.—A single Whip-swimmer (Euglena striata), greatly magnified. Above a thread-like lashing whip is visible; in the centre the round cellular kernel, with its kernel speck.
The Whip-swimmers (Flagellata), which we consider as a third class of the kingdom Protista, are of no less doubtful nature than the Amœbæ. They often show as close and important relations to the vegetable as to the animal kingdom. Some Flagellata at an early stage, when freely moving about, cannot be distinguished from real plants, especially from the spores of many Algæ; whereas others are directly allied to real animals, namely, to the fringed Infusoria (Ciliata). The Flagellata are simple cells which live in fresh or salt water, either singly or united in colonies. The characteristic part of their body is a very movable simple or compound whip-like appendage (whip, or flagellum) by means of which they actively swim about in the water. This class is divided into two orders. Among the fringed whip-swimmers (Cilioflagellata) there exists, in addition to the long whip, a short fringe of vibrating hairs, which is wanting in the unfringed whip-swimmers (Nudoflagellata). To the former belong the flint-shelled yellow Peridinia, which are largely active in causing the phosphorescence of the sea; to the latter belong the green Euglenæ, immense masses of which frequently make our ponds in spring quite green.
Fig. 12.—The Norwegian Flimmer-ball (Magosphæra planula) swimming by means of its vibratile fringes, as seen from the surface.
A very remarkable new form of Protista, which I have named Flimmer-ball (Magosphæra), I discovered only three years ago (in September, 1869), on the Norwegian coast (Fig. 12), and have more accurately described in my Biological Studies[(15)] (p. 137, Plate V.). Off the island of Gis-oe, near Bergen, I found swimming about, on the surface of the sea, extremely neat little balls composed of a number (between thirty and forty) of fringed pear-shaped cells, the pointed ends of which were united in the centre like radii. After a time the ball dissolved. The individual cells swarmed about independently in the water like fringed Infusoria, or Ciliata. These afterwards sank to the bottom, drew their fringes into their bodies, and gradually changed into the form of creeping Amœbæ (like Fig 10 B). These last afterwards encased themselves (as in Fig. 10 A), and then divided by repeated halvings into a large number of cells (exactly as in the case of the cleavage of the egg, Fig. 6, vol. i. p. [299]). The cells became covered with vibratile hairs, broke through the case enclosing them, and now again swam about in the shape of a fringed ball (Fig. 12). This wonderful organism, which sometimes appears like a simple Amœba, sometimes as a single fringed cell, sometimes as a many-celled fringed ball, can evidently be classed with none of the other Protista, and must be considered as the representative of a new independent group. As this group stands midway between several Protista, and links them together, it may bear the name of Mediator, or Catallacta.
Fig. 13.—Labyrinthula macrocystis (much enlarged). Below is a large group of accumulated cells, one of which, on the left, is separating itself; above are two single cells which are gliding along the threads of the retiform labyrinth which form their “tramways.”
The Protista of the fifth class, the Tram-weavers, or Labyrinthuleæ, are of a no less puzzling nature; they were lately discovered by Cienkowski on piles in sea water (Fig. 13). They are spindle-shaped cells, mostly of a yellow-ochre colour, which are sometimes united into a dense mass, sometimes move about in a very peculiar way. They form, in a manner not yet explained, a retiform frame of entangled threads (compared to a labyrinth), and on the dense filamentous “tramways” of this frame they glide about. From the shape of the cells of the Labyrinthuleæ we might consider them as the simplest plants, from their motion as the simplest animals, but in reality they are neither animals nor plants.
Fig. 14.—Navicula hippocampus (greatly magnified). In the middle of the cell the cell-kernel (nucleus) is visible, together with its kernel speck (nucleolus).
The Flint-cells (Diatomeæ), a sixth class of Protista, are perhaps the most closely related to the Labyrinthuleæ. These primary creatures—which at present are generally considered as plants, although some celebrated naturalists still look upon them as animals—inhabit the sea and fresh waters in immense masses, and offer an endless variety of the most elegant forms. They are mostly small microscopic cells, which either live singly (Fig. 14), or united in great numbers, and occur either attached to objects, or glide and creep about in a peculiar manner. Their soft cell-substance, which is of a characteristic brownish yellow colour, is always enclosed by a solid and hard flinty shell, possessing the neatest and most varied forms. This flinty covering is open to the exterior only by one or two slits, through which the enclosed soft plasma-body communicates with the outer world. The flinty cases are found petrified in masses, and many rocks—for example, the Tripoli slate polish, the Swedish mountain meal, etc.,—are in a great measure composed of them.
Fig. 15.—A stalked fruit-body (spore-bladder, filled with spores) of one of the Myxomycetes (Physarum albipes) not much enlarged.
A seventh class of Protista is formed by the remarkable Slime-moulds (Myxomycetes). They were formerly universally considered as plants, as real Fungi, until ten years ago the botanist De Bary, by discovering their ontogeny, proved them to be quite distinct from Fungi, and rather to be akin to the lower animals. The mature body is a roundish bladder, often several inches in size, filled with fine spore-dust and soft flakes (Fig. 15), as in the case of the well-known puff-balls (Gastromycetes). However, the characteristic cellular threads, or hyphæ, of a real fungus do not arise from the germinal corpuscles, or spores, of the Myxomycetes, but merely naked masses of plasma, or cells, which at first swim about in the form of Flagellata (Fig. 11), afterwards creep about like the Amœbæ (Fig. 10 B), and finally combine with others of the same kind to form large masses of “slime,” or “plasmodia.” Out of these, again, there arises, by-and-by, the bladder-shaped fruit-body. Many of my readers probably know one of these plasmodia, the Æthalium septicum, which in summer forms a beautiful yellow mass of soft mucus, often several feet in breadth, known by the name of “tan flowers,” and penetrates tan-heaps and tan-beds. At an early stage these slimy, freely-creeping Myxomycetes, which live for the most part in damp forests, upon decaying vegetable substances, bark of trees, etc., are with equal justice or injustice declared by zoologists to be animals, while in the mature, bladder-shaped condition of fructification they are by botanists defined as plants.
The nature of the Ray-streamers (Rhizopoda), the eighth class of the kingdom Protista, is equally obscure. These remarkable organisms have peopled the sea from the most ancient times of the organic history of the earth, in an immense variety of forms, sometimes creeping at the bottom of the sea, sometimes swimming on the surface. Only very few live in fresh water (Gromia, Actinosphærium). Most of them possess solid calcareous or flinty shells of an extremely beautiful construction, which can be perfectly preserved in a fossil state. They have frequently accumulated in such huge numbers as to form mountain masses, although the single individuals are very small, and often scarcely visible, or completely invisible to the naked eye. A very few attain the diameter of a few lines, or even as much as a couple of inches. The name which the class bears is given because thousands of exceedingly fine threads of protoplasm radiate from the entire surface of their naked slimy body; these rays are quasi-feet, or pseudopodia, which branch off like roots (whence the term Rhizopoda, signifying root-footed), unite like nets, and are observed continually to change form, as in the case of the simpler plasmic feet of the Amœboidea, or Protoplasts. These ever-changing little pseudo-feet serve both for locomotion and for taking food.
The class of the Rhizopoda is divided into three different legions, viz. the chamber-shells, or Acyttaria, the sun-animalcules, or Heliozoa, and the basket-shells, or Radiolaria. The Chamber-shells (Acyttaria) constitute the first and lowest of these three legions; for the whole of their soft body consists merely of simple mucous or slimy cell-matter, or protoplasm, which has not differentiated into cells. However, in spite of this most primitive nature of body, most of the Acyttaria secrete a solid shell composed of calcareous earth, which presents a great variety of exquisite forms. In the more ancient and more simple Acyttaria this shell is a simple chamber, bell-shaped, tubular, or like the shell of a snail, from the mouth of which a bundle of plasmic threads issues. In contrast to these single-chambered forms (Monothalamia), the many-chambered forms (Polythalamia)—to which the great majority of the Acyttaria belong—possess a house, which is composed in an artistic manner of numerous chambers. These chambers sometimes lie in a row one behind the other, sometimes in concentric circles or spirals, in the form of a ring round a central point, and then frequently one above another in many tiers, like the boxes of an amphitheatre. This formation, for example, is found in the nummulites, whose calcareous shells, of the size of a lentil, have accumulated to the number of millions, and form whole mountains on the shores of the Mediterranean. The stones of which some of the Egyptian pyramids are built consist of such nummulitic limestone. In most cases the chambers of the shells of the Polythalamia are wound round one another in a spiral line. The chambers are connected with one another by passages and doors, like rooms of a large palace, and are generally open towards the outside by numerous little windows, out of which the plasmic body can stream or strain forth its little pseudo-feet, or rays of slime, which are always changing form. But in spite of the exceedingly complicated and elegant structure of this calcareous labyrinth, in spite of the endless variety in the structure and the decoration of its numerous chambers, and in spite of the regularity and elegance of their execution, the whole of this artistic palace is found to be the secreted product of a perfectly formless, slimy mass, devoid of any component parts! Verily, if the whole of the recent anatomy of animal and vegetable textures did not support our theory of plastids, if all its important results did not unanimously corroborate the fact that the whole miracle of vital phenomena and vital forms is traceable to the active agency of the formless albuminous combinations of protoplasm, the Polythalamia alone would secure the triumph of that theory. For we may here at any moment, by means of the microscope, point out the wonderful fact, first established by Dujardin and Max Schulze, that the formless mucus of the soft plasma-body, this true “matter of life,” is able to secrete the neatest, most regular, and most complicated structures. This secretive skill is simply a result of inherited adaptation, and by it we learn to understand how this same “primæval slime”—this same protoplasm—can produce in the bodies of animals and plants the most different and most complicated cellular forms.
It is, moreover, a matter of special interest that the most ancient organism, the remains of which are found in a petrified condition, belongs to the Polythalamia. This organism is the “Canadian Life’s-dawn” (Eozoon canadense), which has already been mentioned, and which was found a few years ago in the Ottawa formation (in the deepest strata of the Laurentian system), on the Ottawa river in Canada. If we expected to find organic remains at all in these most ancient deposits of the primordial period, we should certainly look for such of the most simple Protista as are covered with a solid shell, and in the organization of which the difference between animal and plant is as yet not indicated.
We know of but few species of the Sun-animalcules (Heliozoa), the second class of the Rhizopoda. One species is very frequently found in our fresh waters. It was observed even in the last century by a clergyman in Dantzig, Eichhorn by name, and it has been called after him, Actinosphærium Eichhornii. To the naked eye it appears as a gelatinous grey globule of mucus, about the size of a pin’s head. Looking at it through the microscope, we see hundreds or thousands of fine mucous threads radiating from the central plasma body, and perceive that the inner layer of its cell-substance is different from the outer layer, which forms a bladder-like membrane. In consequence of its structure, this, the little sun-animalcule, although wanting a shell, really rises above the structureless Acyttaria, and forms the transition from these to the Radiolaria. The genus Cystophrys is of a nature akin to it.
The Basket-shells (Radiolaria) form the third and last class of the Rhizopoda. Their lower forms are closely allied to the Heliozoa and Acyttaria, whereas their higher forms rise far above them. They are essentially distinguished from both by the fact that the central part of their body is composed of many cells, and surrounded by a solid membrane. This closed “central capsule,” generally of a globular shape, is covered by a mucous layer of plasma, out of which there radiate on all sides thousands of exceedingly fine threads, the branching and confluent so-called pseudopodia. Between these are scattered numerous yellow cells of unknown function, containing grains of starch. Most Radiolaria are characterized by a highly developed skeleton, which consists of flint, and displays a wonderful richness of the neatest and most curious forms. Sometimes this flinty skeleton forms a simple trellice-work ball (Fig. 16 s), sometimes a marvellous system of several concentric trelliced balls, encased in one another, and connected by radial staves. In most cases delicate spikes, which are frequently branched like a tree, radiate from the surface of the balls. In other cases the whole skeleton consists of only one flinty star, and is then generally composed of twenty staves, distributed according to definite mathematical laws, and united in a common central point. The skeletons of other Radiolaria again form symmetrical many-chambered structures, as in the case of the Polythalamia. Perhaps no other group of organisms develop in the formation of their skeletons such an amount of various fundamental forms, such geometrical regularity, and such elegant architecture. Most of the forms as yet discovered, I have given in the atlas accompanying my Monograph of the Radiolaria.[(23)] Here I shall only give as an example the picture of one of the simplest forms, the Cyrtidosphæra echinoides of Nice. The skeleton in this case consists only of a simple trelliced ball (s), with short radial spikes (a), which loosely surround the central capsule (c). Out of the mucous covering, enclosing the latter, radiate a great number of delicate little pseudopodia (p), which are partly drawn back underneath the shell, and fused into a lumpy mass of mucus. Between these are scattered a number of yellow cells (l).
Fig. 16.—Cyrtidosphæra echinoides, 400 times enlarged. c. Globular central capsule. s. Basket-work of the perforated flinty shell. a. Radial spikes, which radiate from the latter. p. The pseudo-feet radiating from the mucous covering surrounding the central capsule. l. Yellow globular cells, scattered between the latter, containing grains of starch.
Most Acyttaria live only at the bottom of the sea, on stones and seaweeds, or creep about in sand and mud by means of their pseudopodia, but most Radiolaria swim on the surface of the sea by means of long pseudopodia extending in all directions. They live together there in immense numbers, but are mostly so small that they have been almost completely overlooked, and have only become accurately known during the last fourteen years. Certain Radiolaria living in communities (Polycyttaria) form gelatinous lumps of some lines in diameter. On the other hand, most of those living isolated (Monocyttaria) are invisible to the naked eye; but still their petrified shells are found accumulated in such masses that in many places they form entire mountains; for example, the Nicobar Islands in the Indian Archipelago, and the Island of Barbadoes in the Antilles.
As most readers are probably but little acquainted with the eight classes of the Protista just mentioned, I shall now add some further general observations on their natural history. The great majority of all Protista live in the sea, some swimming freely on the surface, some creeping at the bottom, and others attached to stones, shells, plants, etc. Many species of Protista also live in fresh water, but only a very small number on dry land (for example, Myxomycetes and some Protoplasta). Most of them can be seen only through the microscope, except when millions of individuals are found accumulated. Only a few of them attain a diameter of some lines, or as much as an inch. What they lack in size of body they make up for by producing astonishing numbers of individuals, and they very considerably influence in this way the economy of nature. The imperishable remains of dead Protista, for instance, the flinty shells of the Diatomeæ and Radiolaria and the calcareous shells of the Acyttaria, often form large rock masses.
In regard to their vital phenomena, especially those of nutrition and propagation, some Protista are more allied to plants, others more to animals. Both in their mode of taking food and in the chemical changes of their living substance, they sometimes more resemble the lower animals, at others the lower plants. Free locomotion is possessed by many Protista, while others are without it; but this does not constitute a characteristic distinction, as we know of undoubted animals which entirely lack free locomotion, and of genuine plants which possess it. All Protista have a soul—that is to say, are “animate”—as well as all animals and all plants. The soul’s activity in the Protista manifests itself in their irritability, that is, in the movements and other changes which take place in consequence of mechanical, electrical, and chemical irritation of their contractile protoplasm. Consciousness and the capability of will and thought are probably wanting in all Protista. However, the same qualities are in the same degree also wanting in many of the lower animals, whereas many of the higher animals in these respects are scarcely inferior to the lower races of human beings. In the Protista, as in all other organisms, the activities of the soul are traceable to molecular motions in the protoplasm.
The most important physiological characteristic of the kingdom Protista lies in the exclusively non-sexual propagation of all the organisms belonging to it. The higher animals and plants multiply almost exclusively in a sexual manner. The lower animals and plants multiply also, in many cases, in a non-sexual manner, by division, the formation of buds, the formation of germs, etc. But sexual propagation almost always exists by the side of it, and often regularly alternates with it in succeeding generations (Metagenesis, vol. i. p. [206]). All Protista, on the other hand, propagate themselves exclusively in a non-sexual manner, and in fact, the distinction of the two sexes among them has not been effected—there are neither male nor female Protista.
The Protista in regard to their vital phenomena stand midway between animals and plants, that is to say, between their lowest forms; and the same must be said in regard to the chemical composition of their bodies. One of the most important distinctions between the chemical composition of animal and vegetable bodies consists in the characteristic formation of the skeleton. The skeleton, or the solid scaffolding of the body in most genuine plants, consists of a substance called cellulose, devoid of nitrogen, but secreted by the nitrogenous cell-substance, or protoplasm. In most genuine animals, on the other hand, the skeleton generally consists either of nitrogenous combinations (chitin, etc.) or of calcareous earth. In this respect some Protista are more like plants, others more like animals. In many of them the skeleton is principally or entirely formed of calcareous earth, which is met with both in animal and vegetable bodies. But the active vital substance in all cases is the mucous protoplasm.
In regard to the form of the Protista, it is to be remarked that the individuality of their body almost always remains at an extremely low stage of development. Very many Protista remain for life simple plastids or individuals of the first order. Others, indeed, form colonies or republics of plastids by the union of several individuals. But even these higher individuals of the second order, formed by the combination of simple plastids, for the most part remain at a very low stage of development. The members of such communities among the Protista remain very similar one to another, and never, or only in a slight degree, commence a division of labour, and are consequently as little able to render their community fit for higher functions as are, for example, the savages of Australia. The community of the plastids remains in most cases very loose, and each single plastid retains in a great measure its own individual independence.
A second structural characteristic, which next to their low stage of individuality especially distinguishes the Protista, is the low stage of development of their stereometrical fundamental forms. As I have shown in my theory of fundamental forms (in the fourth book of the General Morphology), a definite geometrical fundamental form can be pointed out in most organisms, both in the general form of the body and in the form of the individual parts. This ideal fundamental form, or type, which is determined by the number, position, combination, and differentiation of the component parts, stands in just the same relation to the real organic form as the ideal geometrical fundamental form of crystals does to their imperfect real form. In most bodies and parts of the bodies of animals and plants this fundamental form is a pyramid. It is a regular pyramid in the so-called “regular radiate” forms, and an irregular pyramid in the more highly differentiated, so-called “bilaterally symmetrical” forms. (Compare the plates in the first volume of my General Morphology, pp. 556-558.) Among the Protista this pyramidal type, which prevails in the animal and vegetable kingdom, is on the whole rare, and instead of it we have either quite irregular (amorphous) or more simple, regular geometrical types; especially frequent are the sphere, the cylinder, the ellipsoid, the spheroid, the double cone, the cone, the regular polygon (tetrahedron, hexahedron, octahedron, dodecahedron, icosahedron), etc. All the fundamental forms of the pro-morphological system, which are of a low rank in that system, prevail in the Protista. However, in many Protista there occur also the higher, regular, and bilateral types, fundamental forms which predominate in the animal and vegetable kingdoms. In this respect some of the Protista are frequently more closely allied to animals (as the Acyttaria), others more so to plants (as the Radiolaria).
With regard to the palæontological development of the kingdom Protista, we may form various, but necessarily very unsafe, genealogical hypotheses. Perhaps the individual classes of the kingdom are independent tribes, or phyla, which have developed independently of one another and independently of the animal and the vegetable kingdoms. Even if we adopt the monophyletic hypothesis of descent, and maintain a common origin from a single form of Moneron for all organisms, without exception, which ever have lived and still live upon the earth, even in this case the connection of the neutral Protista on the one hand with the vegetable kingdom, and on the other hand with the animal kingdom, must be considered as very vague. We must regard them (compare p. [74]) as lower offshoots which have developed directly out of the root of the great double-branched organic pedigree, or perhaps out of the lowest tribe of Protista, which may be supposed to have shot up midway between the two diverging high and vigorous trunks of the animal and vegetable kingdoms. The individual classes of the Protista, whether they are more closely connected at their roots in groups, or only form a loose bunch of root offsets, must in this case be regarded as having nothing to do either with the diverging groups of organisms belonging to the animal kingdom on the right, or to the vegetable kingdom on the left. They must be supposed to have retained the original simple character of the common primæval living thing more than have genuine animals and genuine plants.
But if we adopt the polyphyletic hypothesis of descent, we have to imagine a number of organic tribes, or phyla, which all shoot up by spontaneous generation out of the same ground, by the side of and independent of one another. (Compare p. [75].) In that case numbers of different Monera must have arisen by spontaneous generation whose differences would depend only upon slight, to us imperceptible, differences in their chemical composition, and consequently upon differences in their capability of development. A small number of Monera would then have given origin to the animal kingdom, and, again, a small number would have produced the vegetable kingdom. Between these two groups, however, there would have developed, independently of them, a large number of independent tribes, which have remained at a lower stage of organization, and which have neither developed into genuine plants nor into genuine animals.
A safe means of deciding between the monophyletic and polyphyletic hypotheses is as yet quite impossible, considering the imperfect state of our phylogenetic knowledge. The different groups of Protista, and those lowest forms of the animal kingdom and of the vegetable kingdom which are scarcely distinguishable from the Protista, show such a close connection with one another and such a confused mixture of characteristics, that at present any systematic division and arrangement of the groups of forms seem more or less artificial and forced. Hence the attempt here offered must be regarded as entirely provisional. But the more deeply we penetrate into the genealogical secrets of this obscure domain of inquiry, the more probable appears the idea that the vegetable kingdom and the animal kingdom are each of independent origin, and that midway between these two great pedigrees a number of other independent small groups of organisms have arisen by repeated acts of spontaneous generation, which on account of their indifferent neutral character, and in consequence of their mixture of animal and vegetable properties, may lay claim to the designation of independent Protista.
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N.B.—The lines marked with a ♱ indicate extinct tribes of Protista, which have arisen independently by repeated acts of Spontaneous Generation.
Thus, if we assume one entirely independent trunk for the vegetable kingdom, and a second for the animal kingdom, we may set up a number of independent stems of Protista, each of which has developed, quite independently of other stems and trunks, from a special archigonic form of Monera. In order to make this relation more clear, we may imagine the whole world of organisms as an immense meadow which is partially withered, and upon which two many-branched and mighty trees are standing, likewise partially withered. The two great trees represent the animal and vegetable kingdoms, their fresh and still green branches the living animals and plants; the dead branches with withered leaves represent the extinct groups. The withered grass of the meadow corresponds to the numerous extinct tribes, and the few stalks, still green, to the still living phyla of the kingdom Protista. But the common soil of the meadow, from which all have sprung up, is primæval by protoplasm.