The simplest forms of life—Cell theory and cell dogma—Precellular organisms: monera, cytodes, and cells—Actual monera—Chromacea (cyanophyceÆ)—Chromatophora—Coenobia of chromacea: vital phenomena—Bacteria—Relations of the bacteria to the chromacea, the fungi, and the protozoa—Rhizomonera (protamoeba, protogenes, protomyxa, bathybius)—Problematic monera—Phytomonera (plasmodoma) and zoomonera (plasmophaga)—Transition between the two classes.

In the study and explanation of all complex phenomena the first thing to do is to understand the simple parts, the manner of their combination, and the development of the compound from the simple. This principle applies generally to inorganic objects, such as minerals, artificially constructed machines, etc. It is also of general application in biological work. The efforts of comparative anatomy are directed to the comprehension of the intricate structure of the higher organisms from the rising scale of organization and life in the lower, and the origin of the former by historical development from the latter. The modern science of the cell (cytology), which has in a short time attained a considerable rank, pursues a method in opposition to this principle. The intricate composition of the unicellular organism, in many of the higher protists (such as the ciliata and infusoria) and many of the higher tissue-cells (such as the neurona) has led to the erroneous ascription of a highly complex organization to the cell in general. One would be justified in saying that of late the cell-theory has established itself in the dangerous and misleading position of a cell-dogma.

The modern treatment of the science, as we find it in numbers of recent works, even in some of the most distinguished manuals, and which we must resent on account of its dogmatism, culminates in something like the following theses:

1. The nucleated cell is the general elementary organism; all living things are either unicellular, or made up of a number of cells and tissues.

2. This elementary organism consists of at least two different organs (or, more correctly, organella), the internal nucleus and the outer cell-body (or cytoplasm).

3. The matter in each of these cell-organs—the caryoplasm of the nucleus and the cytoplasm of the body—is never homogeneous (or consisting of a chemical substratum), but always "organized," or made up of several chemically and anatomically different elementary constituents.

4. The plasm (or protoplasm) is, therefore, a morphological, not a chemical, unity.

5. Every cell comes (and has come) only from a mother-cell, and every nucleus from a mother-nucleus (omnis cellula e cellula—omnis nucleus e nucleo).

These five theses of the modern cell-dogma are by no means sound; they are incompatible with the theory of evolution. I have, therefore, consistently resisted them for thirty-eight years, and consider them to be so dangerous that I will briefly give my reasons. First, let us clearly understand the modern definition of the cell. It is now generally defined (in accordance with the second thesis) as being composed of two essentially different parts, the nucleus and the cell-body, and it is added that these organella differ constantly both in respect of chemistry, morphology, and physiology. If that is really so, the cell cannot possibly be the primitive organism; if it were, we should have a miracle at the beginning of organic life on the earth. The theory of natural evolution clearly and distinctly demands that the cell (in this sense) is a secondary development from a simpler, primary, elementary organism, a homogeneous cytode. There are still living to-day very simple protists which do not tally with this definition, and which I designated monera in 1866. As they must necessarily have preceded the real cells, they may also be called "precellular organisms."

The earliest organisms to live on the earth, with which the wonderful drama of life began, can, in the present condition of biological science, only be conceived as homogeneous particles of plasm—biogens or groups of biogens, in which there was not yet the division of nucleus and cell-body which characterizes the real cell. I gave the name "cytodes" to these unnucleated cells in 1866, and joined them with the real nucleated cells under the general head of "plastids." I also endeavored to prove that such cytodes still exist in the form of independent monera, and in 1870 I described in my Monograph on the Monera a number of protists which do not tally with the above definition.

Fifty years ago I made the first careful observations of living monera (protamoeba and protogenes), and described them in my General Morphology (vol. i., pp. 133-5; vol. ii., p. xxii.) as structureless organisms without organs and the real beginnings of organic life. Soon afterwards, during a stay in the Canary Islands, I succeeded in following the continuous life-history of a related organism of the rhizopod type, which behaved like a very simple mycetozoon, but differed in having no nucleus; I have reproduced the picture of it in the first plate of my History of Creation. The description of this orange-red globule of plasm (protomyxa aurantiaca) appeared first in my Monograph on the Monera. Most of the organisms which I comprised under this name exhibited the same movements as true rhizopods (or sarcodina). It was afterwards proved of some of them that there was a nucleus hidden within the homogeneous particle of plasm, and that, therefore, they must be regarded as real cells. But this discovery was wrongly extended to the whole of the monera, and the existence of unnucleated organisms was denied altogether. Nevertheless, there are living to-day several kinds of these organisms without organs, some of them being very widely distributed. The chief examples are the chromacea and the bacteria, the former with vegetal and the latter with animal metabolism (or the former plasmodomous = plasma-forming, and the latter plasmophagous = plasma-feeding). On the ground of this important chemical difference, I distinguished two principal groups of the monera in my Systematic Phylogeny twenty years ago—the phytomonera and the zoomonera, the former being unnucleated protophyta and the latter unnucleated protozoa.

Among living organisms the chromacea are certainly the most primitive and the nearest to the oldest inhabitants of the earth. Their simplest forms, the chroococcacea, are nothing but small structureless particles of plasm, growing by plasmodomism (formation of plasm) and multiplying by simple cleavage as soon as their growth passes a certain limit of individual size. Many of them are surrounded by a thin membrane or somewhat thicker gelatinous covering, and this circumstance had prevented me for some time from counting the chromacea as monera. However, I became convinced afterwards that the formation of a protective cover of this kind around the homogeneous particle of plasm may indeed be regarded from the physiological stand-point as a "purposive" structure, but at the same time may be looked upon, from the purely physical stand-point, as a result of superficial strain. On the other hand, the physiological character of these plasmodomous monera is especially important, as it gives us the simple key to the solution of the great question of spontaneous generation (or archigony, cf. chapter xv.).

The chromacea are to-day found in every part of the earth, living sometimes in fresh water and sometimes in the sea. Many species form blue-green, violet, or reddish deposits on rocks, stones, wood, and other objects. In these thin gelatinous plates millions of small homogeneous cytodes are packed close together. Their tint is due to a peculiar coloring matter (phycocyan), which is chemically connected with the substance of the plasma-particle. The shade of this color differs a good deal in the various species of chromacea (of which more than eight hundred have been distinguished); in the native species it is generally blue-green or sage-green, sometimes blue, cyanine blue, or violet. Hence the common name cyanophyceÆ (i.e., blue algÆ). It is incorrect, for two reasons; firstly, because only a part of these protophyta are blue, and, secondly, because they (as simple, primitive plants without tissue) must be distinguished from the real algÆ (phyceÆ), which are multicellular, tissue-forming plants. Other chromacea are red, orange, or yellow in color, as the interesting trichodesmium erythrÆum, for instance, the flaky masses of which, gathering in enormous quantities, cause at certain times the yellow or red coloring of the sea-water in the tropics; it is these that are responsible for the name "Red Sea" on the Arabian and "Yellow Sea" on the Chinese coast. When I passed the equator in the Sunda Straits on March 10, 1901, the boat sailed through colossal accumulations, several miles in width, of this trichodesmium. The yellow or reddish surface of the water looked as if it were strewn with sawdust. In the same way, the surface of the Arctic Ocean is often colored brown or reddish-brown by masses of the brown procytella primordialis (formerly described as protococcus marinus).

It is clearly quite illogical to regard the chromacea as a class or family of the algÆ, as is still done in most manuals of botany. The real algÆ—excluding the unicellular diatomes and paulotomes, which belong to the protophyta—are multicellular plants that form a thallus or bed of a certain form and characteristic tissue. The chromacea, which have not advanced as far as the real nucleated cell, are unnucleated cytodes of a lower and earlier stage of plant-life. If one would compare the chromacea with algÆ or other plants at all, the comparison cannot be with their constituent cells, but merely with the chromatophora or chromatella, which are found in all green plant-cells, and form part of their contents. To be more precise, these green granules of chlorophyll must be regarded as organella of the plant-cell, or separated plasma-formations which arise beside the nucleus in the cytoplasm. In the embryonic cells of the germs of plants and in their vegetation points the chromatophora are as yet colorless, and are developed, as solid, very refractive, globular, or roundish granules, from the firm layer of plasm which immediately surrounds the nucleus. Afterwards they are converted, by a chemical process, into the green chlorophyll granules or chloroplasts, which have the most important function in the plasmodomism or carbon-assimilation of the plant.

The fact that the green chlorophyll granules grow independently within the living plant-cell and multiply by segmentation is very important and interesting. The globular chloroplasts are constricted in the middle, and split into two equal daughter-globules. These daughter-plastids grow, and multiply in turn in the same way. Hence they behave within the plant-cell just like the free-living chromacea in the water. On the strength of this significant comparison, one of our ablest and most open-minded scientists, Fritz MÜller-Desterro, of Brazil, pointed out in 1893 that we may see in every green vegetal cell a symbiosis between plasmodomous green and plasmophagous not-green companions (cf. my Anthropogeny, figs. 277 and 278, and in the text).

Many species of the simplest chromacea live as monobia (individually). When the tiny plasma globules have split into two equal halves by simple segmentation, they separate, and live their lives apart. This is the case with the common, ubiquitous chroococcus. However, most species live in common, the plasma granules forming more or less thick coenobia, or communities or colonies of cells. In the simplest case (aphanocapsa) the social cytodes secrete a structureless gelatinous mass, in which numbers of blue-green plasma globules are irregularly distributed. In the gloeocapsa, which forms a thin blue-green gelatinous deposit on damp walls and rocks, the constituent cytodes cover themselves immediately after cleavage with a fresh gelatinous envelope, and these run together into large masses. But the majority of the chromacea form firm, threadlike cell communities or chains of plastids (catenal coenobia.) As the transverse cleavage of the rapidly multiplying cytodes always follows the same direction, and the new daughter-cytodes remain joined at the cleavage surfaces, and are flattened into discoid shape, we get stringlike formations or articulated threads of considerable length, as in the oscillaria and nostochina. When a number of these threads are joined together in gelatinous masses, we often get large, irregular, jelly-like bodies, as in the common "shooting-star jellies" (nostoc communis). They attain the size of a plum.

In view of the extreme importance which I attach to the chromacea as the earliest and simplest of all organisms, it is necessary to put clearly the following facts with regard to their anatomic structure and physiological activity:

1. The organism of the simplest chromacea is not composed of different organella or organs; and it shows no trace of purposive construction or definite architecture.

2. The homogeneous tinted plasma granule which makes up the entire organism in the simplest case (chroococcus) exhibits no plasma structure (honeycomb, threads, etc.) whatever.

3. The original globular form of the plasma particle is the simplest of all fundamental types, and is also that assumed by the inorganic body (such as a drop of rain) in a condition of stable equilibrium.

4. The formation of a thin membrane at the surface of the structureless plasma granule may be explained as a purely physical process—that of surface strain.

5. The gelatinous envelope which is secreted by many of the chromacea is also formed by a simple physical (or chemical) process.

6. The sole essential vital function that is common to all the chromacea is self-maintenance, and growth by means of their vegetal metabolism, or plasmodomism (=carbon assimilation); this purely chemical process is on a level with the catalysis of inorganic compounds (chapter x.).

7. The growth of the cytodes, in virtue of their continuous plasmodomism, is on a level with the physical process of crystal growth.

8. The reproduction of the chromacea by simple cleavage is merely the continuation of this simple growth process, when it passes the limit of individual size.

9. All the other vital phenomena which are to be seen in some of the chromacea can also be explained by physical or chemical causes on mechanical principles. Not a single fact compels us to assume a "vital force."

Especially noteworthy in regard to the physiological character of these lowest organisms are their bionomic peculiarities, especially the indifference to external influences, higher and lower temperatures, etc. Many of the chromacea live in hot springs, with a temperature of fifty to eighty degrees centigrade, in which no other organism is found. Other species may remain for a long time frozen in ice, and resume their vital activity as soon as it thaws. Many chromacea may be completely dried up, and then resume their life if put in water after several years.

Next in order to the chromacea we have the bacteria, the remarkable little organisms which have been well known in the last few decades as the causes of fatal diseases, and the agents of fermentation, putrefaction, etc. The special science which is concerned with them—modern bacteriology—has attained so important a position in a short period—especially as regards practical and theoretical medicine—that it is now represented by separate chairs at most of the universities. We may admire the penetration and the perseverance with which scientists have succeeded, with the aid of the best modern microscopes and methods of preparation and coloring, in making so close a study of the organism of the bacteria, determining their physiological properties, and explaining their great importance for organic life by careful experiments and methods of culture. The bionomic or economic position of the bacteria in nature's household has thus secured for these tiny organisms the greatest scientific and practical interest.

However, we find that certain general views have been maintained by specialists in bacteriology up to our own time which are in curious contrast with these brilliant results. The biologist who studies the systematic relations of the bacteria from the modern point of view of the theory of descent is bewildered at the extraordinary views as to the place of the bacteria in the plant-world (as segmentation-fungi), their relations to other classes of plants, and the formation of their species. When we carefully consider the morphological properties that are common to all true bacteria and compare them with other organisms, we are forced to the conclusion that I urged years ago in various writings: the bacteria are not real (nucleated) cells, but unnucleated cytodes of the rank of the monera; they are not real (tissue-forming) fungi, but simple protists; their nearest relatives are the chromacea.

The individual organisms of the simplest kind, which bacteriologists call "bacteria-cells," are not real nucleated cells. That is the clear negative result of a number of most careful investigations which have been made up to date with the object of finding a nucleus in the plasma-body of the bacteria. Among recent exact investigations we must especially note those of the botanist Reinke, of Kiel, who sought in vain to detect a nucleus in one of the largest and most easily studied genera of the bacteria, the beggiatoa, using every modern technical aid. His conviction that this important cell-structure is really lacking is the more valuable, as it is very prejudicial to his own theory of "dominants." Other scientists (especially Schaudinn) have recently claimed, as equivalent to a nucleus in some of the larger bacteria, a number of very small granules, which are irregularly distributed in the plasm, and are strongly tinted under certain coloring processes. But even if the chemical identity of these substances which take the same color were proved—which is certainly not the case—and even if the appearance of scattered nuclein-granules in the plasm could be regarded as a preliminary to, or a beginning of, the differentiation of an individual, morphologically distinct nucleus, we should not yet have shown its independence as an organellum of the cell.

Nor is this any more proved from the circumstance that in some bacteria (not all) we find a severance of the plasm into an inner and outer layer, or a frothy structure with vacuole-formation, or a special sharply outlined membrane on the plastid. Many bacteria (but not all) have such a membrane, like the nearly related chromacea, and also the secretion of a gelatine envelope. Both classes have also in common an exclusively monogenetic reproduction. The bacteria multiply, like the chromacea, by simple segmentation; as soon as the structureless plasma-granule has reached a certain size by simple growth, it is constricted and splits into two halves. In the long-bodied bacteria (the rod-shaped bacilli) the constriction always goes through the middle of the long axis, and is, therefore, simple transverse cleavage. Many bacteria have also been said to multiply by the formation of spores. But these so-called "spores" are really permanent quiescent forms (without any multiplication of individuals); the central part of the plastid (endoplasm) condenses, separates from the peripheral part (exoplasm), and undergoes a chemical change which makes it very indifferent to external influences (such as a high temperature).

The great majority of the bacteria differ so little morphologically from the chromacea that we can only distinguish these two classes of monera by the difference in their metabolism. The chromacea, as protophyta, are plasmodomous. They form new plasm by synthesis and reduction from simple inorganic compounds—water, carbonic acid, ammonia, nitric acid, etc. But the bacteria, as protozoa, are plasmophagous. They cannot, as a rule, form new plasm, but have to take it from other organisms (as parasites, saprophytes, etc.); they decompose it by analysis and oxydation. Hence the colorless bacteria are without the important green, blue, or red coloring matter (phycocyan) which tints the plastids of the chromacea, and is the real instrument of the carbon-assimilation. However, there are exceptions in this respect: bacillus virens is tinted green with chlorophyll, micrococcus prodigiosus is blood-red, other bacteria purple, and so on. Certain earth-dwelling bacteria (nitro-bacteria) have the vegetal property of plasmodomism; they convert ammonia by oxydation into nitrous acid, and this into nitric acid, using as their source of carbon the carbonic acid gas in the atmosphere. They are thus quite independent of organic substances, and feed, like the chromacea, on simple inorganic compounds.

Hence the affinity between the plasmodomous chromacea and plasmophagous bacteria is so close that it is impossible to give a single safe criterion that will effectually separate the two classes. Many botanists accordingly combine both groups in a single class with the name of schizophyta, and within this distinguish as "orders" the blue-green chromacea as schizophycÆ (cleavage-algÆ) and the colorless bacteria as schizomycetes (cleavage-fungi). However, we must not take this division too rigidly; and the absolute lack of a nucleus and tissue-formation separates the chromacea just as widely from the multicellular tissue-forming algÆ as the bacteria from the fungi. The simple multiplication by the halving of the cell, which is expressed in the name "cleavage-plants" (schizophyta), is also found in many other protists.

The number of forms that can be distinguished as species in the technical sense is very great in the case of the bacteria, in spite of the extreme simplicity of their outward appearance; many biologists speak of several hundred, and even of more than a thousand, species. But when we look solely to the outer form of the living plasma-granule, we can only distinguish three fundamental types: (1) Micrococci, or spherobacteria (briefly, cocci), globular or ellipsoid; (2) bacilli, or rhabdo-bacteria (also called eubacteria, or bacteria in the narrower sense), rod-shaped, cylindrical, and often twisted like worms (comma-bacilli); (3) spirilla, or spirobacteria, screw-shaped rods (vibriones when the screw is slight, and spirochÆta when it has many coils). Besides this threefold difference in the forms of the cytodes, we have a ground of distinction in many bacilli and spirilla in the possession of one or more very thin lashes (flagella), which proceed from one of both poles of the lengthened plastid. The construction and vibration of these serves for locomotion in the swimming bacteria; but they are only found for a time in many species, and in many others are altogether wanting.

Since, then, neither the simple outer form of the bacterium-cytodes nor their homogeneous internal structure provides a satisfactory ground for the systematic distinction of the numerous species, their physiological properties are generally used for the purpose, especially their different behavior towards organic foods (albumin, gelatine, etc.), their chemical actions, and the various effects of poisoning and decomposition which they produce in the living organism. No bacteriologist now doubts that all the vital activities of the bacteria are of a chemical nature, and precisely on this account these microbes are of extreme importance. When we bear in mind how complicated are the relations of the various species of bacteria to the tissues of the human body, in which they cause the diseases of typhus, hypochondriasis, cholera, and tuberculosis, we are bound to admit that the real cause of these maladies must be sought in the peculiar molecular structure of the bacterium-plasm, or the particular arrangement of its molecules and the innumerable atoms (more than a thousand) which are, in a very loose way, made up into special groups of molecules. The chemical products of their mutual action are what we call ptomaines, which are partly very virulent poisons (toxins). We have succeeded in producing several of these poisonous matters in large quantities by artificial culture, and isolating them and experimentally ascertaining their nature; as, for instance, tetanin, which causes tetanus, typhotoxin, the poison of typhus, etc.

In thus declaring the action of bacteria to be purely chemical and analogous to that of well-known inorganic poisons, I would particularly point out that this very justifiable statement is a pure hypothesis; it is an excellent illustration of the fact that we cannot get on in the explanation of the most important natural phenomena without hypotheses. We can see nothing whatever of the chemical molecular structure of the plasm, even under the highest power of the microscope; it lies far below the limit of microscopic perception. Nevertheless, no expert scientist has the slightest doubt of its existence, or that the complicated movements of the sensitive atoms and the molecules and groups of molecules they make up are the causes of the vast changes which these tiny organisms effect in the tissues of the human and the higher animal body.

Moreover, the distinction of the many species of bacteria is of interest in connection with the general question of the nature and constancy of a species. Whereas formerly in biological classification only definite morphological characters, or definable differences in outer form or inner structure, were regarded as of any moment in the distinction of species, here, in view of the vagueness or total lack of these characters, we have to look mainly to the physiological properties, and these are based on the chemical differences in their hypothetical molecular structure. But even these are not absolutely constant; on the contrary, many bacteria lose their specific qualities by progressive culture under changed food-conditions. By a change in the temperature and the nutritive field in which a number of poisonous bacteria have been reared, or by the action of certain chemicals, not only the growth and multiplication are altered, but also the injurious effect they have on other organisms by the generation of poisons. This poisonous effect is weakened, and—what is most important—the weakening is transmitted by heredity to the following generations. On this is based the familiar process of inoculation, an admirable example of the inheritance of acquired characteristics.

As the bacteria are still often described as "cleavage-fungi" and classified along with the real fungi, we must particularly point out the wide gulf that separates the two groups. The real fungi (or mycetes) are metaphyta, their multicellular body (thallus) forming a very characteristic sort of tissue, the mycelium; this is composed of a number of interlaced and interwoven threads (or hyphens). Each fungus-thread consists of a row of lengthened cells, which have a thin membrane and enclose a number of small nuclei in the colorless plasm. Moreover, the two sub-classes of the real fungi, the ascomycetes and basimycetes, form peculiar fruit-bodies which generate spores (ascodia and basidia). There is no trace whatever of these real characteristics of the true fungus in the bacteria. Nor is it less incorrect to class them with the fungilli, the so-called unicellular fungi or phycomycetes (ovomycetes and zygomycetes); these form a special class of protists which has the closest affinity to the gregarinÆ.

Like the closely related chromacea, many of the bacteria show a marked tendency to form communities or cell-colonies. These cell-communities arise, as elsewhere, from the fact that the individuals, which multiply rapidly by continuous cleavage, remain joined together. This may happen in two ways. When the social bacteria secrete large quantities of gelatine, and remain distributed in this, we have the zoogloea (as in the case of the aphanocapsa and gloeocapsa among the chromacea). If, on the other hand, the long-bodied bacilli remain fastened together in rows, we get the knotted threads of leptothrix and beggiatoa (which may be compared with the oscillaria). And, if these threads go into branches, we have cladothrix. Other coenobia of bacteria have the appearance of disks, the cytodes dividing in a plane, usually in groups of four (as in merismopedia), or of cube-shaped packets when they are in all three directions of space (sarcina).

The two classes of bacteria and chromacea seem, in the present condition of our knowledge, on account of their simple organization, to be the simplest of all living things, real monera, or organisms without organs. Hence we have to put them at the lowest stage of the protist kingdom, and must regard the difference between them and the most highly differentiated unicellular beings (such as the radiolaria, ciliated infusoria, diatomes, or siphonea) as no smaller than the difference (in the realm of the histona) between a lower polyp (hydra) and a vertebrate, or between a simple alga (ulva) and a palm. But if the kingdom of the protists is badly divided, on the older rule, into a plant kingdom and an animal kingdom, the only discriminating mark we have left is the difference in metabolism; in that case we have to include the plasmophagous bacteria in the animal kingdom (as Ehrenberg did in 1838) and the plasmodomous chromacea in the plant kingdom. The remarkable class of the flagellata, which includes ciliated unicellulars of both groups, contains several forms which are only distinguished from the typical bacterium by the possession of a nucleus. If it is true that in some of the protists which were counted as bacteria a real nucleus has been detected, these must be separated from the others (unnucleated) and included in the nucleated flagellata.

The monera which I described in 1866, and on which I based the theory of the monera in my monograph, belong to a different division of the protists from the classes of bacteria and chromacea. These are the forms which I described as protamoeba, protogenes, protomyxa, etc. Their naked mobile plasma-bodies thrust out pseudopodia, or variable "false feet," from their surface, like the (nucleated) real rhizopods (=sarcodinÆ); but they differ essentially from the latter in the absence of a nucleus. Afterwards (in my Systematic Phytogeny) I proposed to separate these unnucleated rhizopods from the others, giving the name of lobomonera (protamoeba) to the amoeba-like monera with flap-shaped feet, and the name of rhizomonera (protomyxa, pontomyxa, biomyxa, arachnula, etc.) to the gromia-like, root-feet forming monera. However, of late years, real nuclei have been detected in each of these large monera, and so they have been proved to be true cells. This discovery was made possible by the improved modern methods of coloring the nucleus which I had not the use of thirty years ago in my first observations. On the strength of these recent discoveries many scientists claim that all the monera I described are true cells, and must have nuclei. This baseless assertion is much employed by the opponents of the theory of evolution in order to deny the existence of the monera altogether.

Of the genus of monera which we call protamoeba I have given an illustration in my History of Creation (tenth edition), which has been frequently reproduced. Several species (at least two or three) of this genus still exist, and are distinguished by the shape of their flap-formation and their method of motion. They resemble ordinary simple amoebÆ, and only differ from these to any extent in the absence of a nucleus. The protamoeba primitiva seems to be pretty widely distributed; it has been found repeatedly by observers (Gruber, Cienkowski, Leidy, etc.) in inland waters. In the zoological demonstrations which I have given at the University of Jena for forty years, and in the course of which the lowly inhabitants of our fresh water are regularly examined with the microscope, the protamoeba primitiva has been found four or five times. It always had the same form, as I described it, moved about by the slow formation of flaps at its surface, multiplied by simple cleavage, and showed no trace of a nucleus in its homogeneous plasma-body even with the most careful application of the modern methods of tinting the nucleus. A larger number of very fine granules (microsoma) that were irregularly distributed in the plasm, and were more or less colored by nucleus-reagents, cannot be reckoned as clear equivalents of the nucleus in this or in similar cases; they are probably products of metabolism. The same may be said of the larger marine form of rhizomoneron, which A. Gruber has recently called pelomyxa pallida.

The large marine form of rhizomoneron to which Huxley gave the name of bathybius Haeckelii in 1868, and as to the real nature of which many opinions have been expressed, seems, according to the latest investigation, not to have the significance ascribed to it. However, the much-discussed question of the bathybius is superfluous as far as our monera theory and the associated hypothesis of archigony (chapter xv.) are concerned, since we have now a better knowledge of the much more important monera-forms of the chromacea and bacteria.

In the case of some of the protists I described in my Monograph on the Monera, it is at present doubtful whether their plasma-body contains a nucleus or not, and, therefore, whether they are to be classed as true cells or cytodes. This applies especially to the forms which only happened to come under observation once, such as protomyxa and myxastrum. In these obscure cases we must wait for fresh investigations and the application of the modern methods of tinting the nucleus. I may, however, point out, in passing, that these famous methods of nucleus-coloring give by no means the absolute certainty which is ascribed to them; there are other substances which take color in the same way as chromatin. As far as my monera theory is concerned, or the great general importance which I attach to these unnucleated living granules of plasm, it does not matter whether a nucleus is detected in these problematic monera or not. The chromacea alone—the most important of all monera—completely suffice to provide a base for the far-reaching theoretical conclusions which I draw from it.

At the close of these observations on the monera I will briefly recapitulate the weighty inferences which we can deduce from their simple organization. They serve as a solid foundation for the chief theses of our monistic biology; and they are inconsistent with the dualistic views of modern vitalists. In the first place, I emphasize the fact that the structureless plasm-body of the simple monera has no sort of organization and no composition from dissimilar parts co-operating for definite vital aims. Reinke's conscious "dominant"—as well as Weismann's mechanical "determinants"—have nothing to do here. The whole vital activity of the simplest monera, especially of the chromacea, is confined to their metabolism, and is therefore a purely chemical process, that may be compared to the catalysis of inorganic compounds. The simple formation of individuals in this primitive living matter is merely a question of the cleavage of plasma globules of a certain size (chroococcus); and their primitive multiplication (by simple self-division) is only a continued growth (analogous to that of the crystal). When this simple growth passes a certain limit, that is fixed by the chemical constitution, it leads to the independent existence of the redundant growth-products.

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