However, this does not lessen the great value which the actual and faithfully preserved features of that sketch possess. _Ontogeny is of the most inestimable value for the knowledge of the earliest palaeontological conditions of development_, just because no petrified remains of the most ancient conditions of the development of tribes and cla.s.ses have been preserved. These, indeed, could not have been preserved on account of the soft and tender nature of their bodies. No petrifactions could inform us of the fundamental and important fact which ontogeny reveals to us, that the most ancient common ancestors of all the different animal and vegetable species were quite simple cells like the egg-cell. No petrifaction could prove to us the immensely important fact, established by ontogeny, that the simple increase, the formation of cell-aggregates and the differentiation of those cells, produced the infinitely manifold forms of multicellular organisms. Thus ontogeny helps us over many and large gaps in palaeontology.

[Ill.u.s.tration: Hand of Nine different Mammals. Pl. IV.

_1. Man_, _2. Gorilla_, _3. Orang_, _4. Dog_, _5. Seal_, _6. Porpoise_, _7. Bat_, _8. Mole_, _9. Duck-bill_.]

To the invaluable records of creation furnished by palaeontology and ontogeny are added the no less important evidences for the blood relationship of organisms furnished by _comparative anatomy_. When organisms, externally very different, nearly agree in their internal structure, one may with certainty conclude that the agreement has its foundation in Inheritance, the dissimilarity its foundation in Adaptation. Compare, for example, the hands and fore paws of the nine different animals which are represented on Plate IV., in which the bony skeleton in the interior of the hand and of the five fingers is visible.

Everywhere we find, though the external forms are most different, the same bones, and among them the same number, position, and connection. It will perhaps appear very natural that the hand of _man_ (Fig. 1) differs very little from that of the _gorilla_ (Fig. 2) and of the _orang-outang_ (Fig. 3), his nearest relations. But it will be more surprising if the fore feet of the _dog_ also (Fig. 4), as well as the breast-fin (the hand) of the _seal_ (Fig. 5), and of the _dolphin_ (Fig.

6), show essentially the same structure. And it will appear still more wonderful that even the wing of the _bat_ (Fig. 7), the shovel-feet of the _mole_ (Fig. 8), and the fore feet of the _duck-bill_ (Ornithorhynchus) (Fig. 9), the most imperfect of all mammals, is composed of entirely the same bones, only their size and form being variously changed. Their number, the manner of their arrangement and connection has remained the same. (Compare also the explanation of Plate IV., in the Appendix.) It is quite inconceivable that any other cause, except the common inheritance of the part in question from common ancestors, could have occasioned this wonderful h.o.m.ology or similarity in the essential inner structure with such different external forms.

Now, if we go down further in the system below the mammals, and find that even the wings of birds, the fore feet of reptiles and amphibious animals, are composed of essentially the same bones as the arms of man and the fore legs of the other mammals, we can, from this circ.u.mstance alone, with perfect certainty, infer the common origin of all these vertebrate animals. Here, as in all other cases, the degree of the internal agreement in the form discloses to us the degree of blood relationship.

CHAPTER XVI.

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 Primaeval Beings.-Eight Cla.s.ses of the Protista Kingdom.-Monera, Ambae, or Protoplastae.-Whip-swimmers, or Flagellata.-Ciliated-b.a.l.l.s, or Catallacta.-Labyrinth-streamers, or Labyrinthuleae.-Flint-cells, or Diatomeae.-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 palaeontological 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, palaeontology, 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, palaeontological, 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 palaeontological 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, alb.u.minous 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 palaeontological doc.u.ments, 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 palaeontological 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 alb.u.minous const.i.tution, in which another alb.u.minous corpuscle, the cell-kernel, is enclosed.

This cell containing its kernel grows and becomes enlarged. By division it forms an acc.u.mulation 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 palaeontological 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 palaeontological development of its chain of ancestors, we may at once, with full a.s.surance, draw the simple and important conclusion, that _all many-celled animals and plants were originally derived from single-celled organisms_. The primaeval 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 a.s.sert 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 s.p.a.ce 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 a.s.surance 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 primaeval "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 "primaeval cell." But where did those few "original cells," or the one primaeval 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 primaeval creatures of the simplest kind conceivable, like the still living Protambae, Protomyxae, etc. (vol. i. p. 186, Fig. 1). Only such corpuscules of mucus without component parts-whose whole alb.u.minous body is as h.o.m.ogeneous 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 alb.u.minous ma.s.s 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 primaeval mucus of the Moneron body, by the formation of a kernel in the interior and a covering on the outer surface of the ma.s.s 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 pa.s.s 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 cla.s.ses," or "main cla.s.ses,"

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 a.s.sumes either four or five. In the animal kingdom these tribes would essentially coincide with those four, five, or six main divisions which zoologists, since Bar and Cuvier, have distinguished as "main forms, general plans, branches, or sub-kingdoms" of the animal kingdom.

(Compare vol. i. p. 53.) Bar 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 cla.s.ses which modern botany distinguishes in the vegetable kingdom, namely:-1. Flowering plants (Phanerogamia); 2. Ferns (Filicinae); 3. Mosses (Muscinae); 4. Lichens (Lichenes); 5. Fungi (Fungi); and 6. Water-weeds (Algae). 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 cla.s.ses, 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 cla.s.ses 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 primaeval 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 a.s.sume 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 a.s.sume that several different species of Monera have arisen by spontaneous generation, and that these gave rise to several different main cla.s.ses (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 ma.s.s, without component particles, made up of a single alb.u.minous 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 alb.u.minous combination. But these subtle and complicated differences of mixture of the infinitely manifold combinations of alb.u.men 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 primaeval home for most species (which has already been discussed), we may be permitted to a.s.sume 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 a.s.sume 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 cla.s.ses, 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 a.s.signed 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 a.s.signed 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 a.s.signed 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 a.s.sign 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 a.s.sign the individual cla.s.ses 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 cla.s.ses of the kingdom Protista, we may at present distinguish the following:-

1. The still living Monera; 2. The Amboidea, or Protoplasts; 3. The Whip-swimmers, or Flagellata; 4. The Flimmer-b.a.l.l.s, or Catallacta; 5.

The Tram-weavers, or Labyrinthuleae; 6. The Flint-cells, or Diatomeae; 7.

The Slime-moulds, or Myxomycetes; 8. The Ray-streamers, or Rhizopoda.

The most important groups at present distinguishable in these eight cla.s.ses 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 cla.s.ses named we have become intimately acquainted only during the last ten years. The exceedingly interesting Monera and Labyrinthuleae, 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 cla.s.ses 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 cla.s.ses specified, and many other unknown cla.s.ses 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 cla.s.ses of protista as the lower small off-shoots 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 cla.s.ses of protista given on the next page, and their general natural history.

SYSTEMATIC SURVEY

_Of the Larger and Smaller Groups of the Kingdom Protista._

----------------+--------------------+------------------+----------------- _Cla.s.ses of | _Systematic Name | _Orders of | _A name of a the Protista | of the Cla.s.ses_. | Families of the | Genus Kingdom._ | | Cla.s.ses._ | as an example._ ----------------+--------------------+------------------+----------------- { 1. Gymnomonera Protogenes 1. MONERS Monera { 2. Lepomonera Protomyxa

{ 1. Gymnambae Amba 2. PROTOPLASTS Amboida { 2. Leptambae Arcella { 3. Gregarinae Monocystis

{ 1. Nudiflagellata Euglena 3. WHIP-SWIMMERS Flagellata { 2. Cilioflagellata Peridinium

4. FLIMMER-b.a.l.l.s Catallacta 1. Catallacta Magosphaera

5. TRAM-WEAVERS Labyrinthuleae 1. Labyrinthuleae Labyrinthula

{ 1. Striata Navicula 6. FLINT-CELLS Diatomea { 2. Vittata Tabellaria { 3. Areolata Coscinodiscus

{ 1. Physareae aethalium 7. SLIME-MOULDS Myxomycetes { 2. Stemoniteae Stemonitis { 3. Trichiaceae Arcyria { 4. Lycogaleae Reticularia

{ I. Acyttaria { 1. Monothalamia Gromia { { 2. Polythalamia Nummulina 8. RAY-STREAMERS { OR RHIZOPODS. { II. Heliozoa 1. Heliozoa Actinosphaerium (Root-feet) { { { 1. Monocyttaria Cyrtidosphaera { III. Radiolaria { 2. Polycyttaria Collosphaera

[Ill.u.s.tration: FIG. 8.-Protamba 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 cla.s.s 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 palaeontological 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 h.o.m.ogeneous little lump of slime or mucus which const.i.tutes 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 a.s.sign them to the animal as it would be to a.s.sign 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 cla.s.s, contrasting them with the other cla.s.ses of the kingdom Protista, as well as with the animal kingdom. Morphologically considered, the Monera-on account of the perfect h.o.m.ogeneity of the alb.u.minous 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 ill.u.s.trations of the forms and vital phenomena of the still living Monera (Protamba, 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 Protamba (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).

[Ill.u.s.tration: FIG. 9.-Bathybius Haeckelii, the "creature of primaeval slime," from the greatest depths of the sea. The figure, which is greatly magnified, only shows that form of the Bathybius which consists of a naked network of protoplasm, without the discoliths and cyatholiths which are found in other forms of the same Moneron, and which perhaps may be considered as the products of its secretion.]

The _Ambae_ of the present day, and the organisms most closely connected with them, _Arcellidae_ and _Gregarinae_, which we here unite as a second cla.s.s of Protista under the name of _Amboidea_ (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, sh.e.l.l-less plastids with a kernel-occur as well among real plants as real animals. The generative cells, for example, in many Algae (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 Medusae). (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 Amba. For an Amba 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 Amba 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 Amba, which perpetually changes its form, pa.s.ses 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_).

[Ill.u.s.tration: FIG. 10.-Amba sphaerococcus, greatly magnified. A fresh-water Amba without a contractile vacuole. _A._ The enclosed Amba 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 Amba, 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_).]