The Riddle of the Universe at the close of the nineteenth century

by Ernst Haeckel

We learn the character of the psychic activity of these unicellular organisms from the comparative physiology of the protists of to-day. Close observation and careful experiment have opened out to us in this respect, in the second half of the nineteenth century, a new world of the most interesting phenomena. The best description of them was given by Max Verworn in his thoughtful work, based on original research, Psycho-physiological Studies of the Protists. The work includes also the few earlier observations of the “psychic life of the protist.” Verworn came to the firm conclusion that the psychic processes are unconscious in all the protists, that the phenomena of sensation and movement coincide with the molecular vital processes in their protoplasm, and that their ultimate causes are to be sought in the properties of the protoplasmic molecules (the plastidules). “Hence the psychic phenomena of the protists form a bridge that connects the chemical processes of the inorganic world with the psychic life of the highest animals; they represent the germ of the highest psychic phenomena of the metazoa and of man.”

The careful observations and many experiments of Verworn, together with those of Wilhelm Engelmann, Wilhelm Preyer, Richard Hertwig, and other more recent students of the protists, afford conclusive evidence for my “theory of the cell-soul” (1866). On the strength of several years of study of different kinds of protists, especially rhizopods and infusoria, I published a theory thirty-three years ago to the effect that every living cell has psychic properties, and that the psychic life of the multicellular animals and plants is merely the sum total of the psychic functions of the cells which build up their structure. In the lower groups (in algæ and sponges, for instance) all the cells of the body have an equal share in it (or with very slight differences); in the higher groups, in harmony with the law of the “division of labor,” only a select portion of them are involved—the “soul-cells.” The important consequences of this “cellular psychology” were partly treated in my work on The Perigenesis of the Plastidule (1876), and partly in my speech at Munich, in 1877, on “Modern Evolution in Relation to the Whole of Science.” A more popular presentation of them is to be found in my two Vienna papers (1878) on “The Origin and Development of the Sense-Organs” and on “Cell-Souls and Soul-Cells.”

Moreover, the cell-soul, even within the limits of the protist world, presents a long series of stages of development, from the most simple and primitive to a comparatively elaborate activity. In the earliest and simplest protists the faculty of sensation and movement is equally distributed over the entire protoplasm of the homogeneous morsel; in the higher forms certain “cell-instruments,” or organella, appear, as their physiological organs. Motor cell-parts of that character are found in the pseudopodia of the rhizopods, and the vibrating hairs, lashes, or cilia of the infusoria. The cell-nucleus, which is wanting in the earlier and lower protists, is considered to be an internal central organ of the cell-life. It is especially noteworthy, from a physiologico-chemical point of view, that the very earliest protists were plasmodomous, with plant-like nutrition—hence protophyta, or primitive plants; from these came as a secondary stage, by metasitism, the first plasmophagi, with animal nutrition—the protozoa, or primitive animals.[18] This metasitism, or circulation of nutritive matter, implies an important psychological advance; with it began the development of those characteristic properties of the animal soul which are wanting in the plant.

We find the highest development of the animal cell-soul in the class of ciliata, or ciliated infusoria. When we compare their activity with the corresponding psychic life of the higher, multicellular animals, we find scarcely any psychological difference; the sensitive and motor organella of these protozoa seem to accomplish the same as the sense-organs, nerves, and muscles of the metazoa. Indeed, we have found in the great cell-nucleus (meganucleus) of the infusoria a central organ of psychic activity, which plays much the same part in their unicellular organism as the brain does in the psychic life of higher animals. However, it is very difficult to determine how far this comparison is justified; the views of experts diverge considerably over the matter. Some take all spontaneous bodily movement in them to be automatic, or impulsive, and all stimulated movement to be reflex; others are convinced that such movements are partly voluntary and intentional. The latter would attribute to the infusoria a certain degree of consciousness, and even self-consciousness; but this is rejected by the others. However that very difficult question may be settled, it does not alter the fact that these unicellular protozoa give proof of the possession of a highly developed “cell-soul,” which is of great interest for a correct decision as to the psyche of our earliest unicellular ancestors.

II. The communal or cenobitic soul (coenopsyche): second stage of phyletic psychogenesis.—Individual development begins, in man and in all other multicellular animals, with the repeated segmentation of one simple cell. This stem-cell, the impregnated ovum, divides first into two daughter cells, by a process of ordinary indirect segmentation; as the process is repeated there arise (by equal division of the egg) successively four, eight, sixteen, thirty-two, sixty-four such new cells, or “blastomeres.” Usually (that is, in the case of the majority of animals) an irregular enlargement sooner or later takes the place of this original regular division of cells. But the result is the same in all cases—the formation of a (generally spherical) cluster of heterogeneous (originally homogeneous) cells. This stage is called the morula (“mulberry,” which it somewhat resembles in shape). Then, as a rule, a fluid gathers in the interior of this aggregate of cells; it changes into a spherical vesicle; all the cells go to its surface, and arrange themselves in one simple layer—the blastoderm. The hollow sphere which is thus formed is the important stage of the “germinal vesicle,” the blastula, or blastosphere.

The psychological phenomena which we directly observe in the formation of the blastula are partly sensations, partly movements, of this community of cells. The movements may be divided into two groups: (1) the inner movements, which are always repeated in substantially the same manner in the process of ordinary (indirect) segmentation of cells (formation of the axis of the nucleus, mitosis, karyokinesis, etc.); (2) the outer movements, which are seen in the regular change of position of the social cells and their grouping for the construction of the blastoderm. We assume that these movements are hereditary and unconscious, because they are always determined in the same fashion by heredity from the earlier protist ancestors. The sensations also fall into two groups: (1) the sensations of the individual cells, which reveal themselves in the assertion of their individual independence and their relation to neighboring cells (with which they are in contact, and partly in direct combination, by means of protoplasmic fibres); (2) the common sensation of the entire community of cells, which is seen in the individual formation of the blastula as a hollow vesicle.

The causal interpretation of the formation of the blastula is given us by the biogenetic law, which explains the phenomena we directly observe to be the outcome of heredity, and relates them to corresponding historical processes which took place long ago in the origin of the earliest protist-cœnobia, the blastæads. But we get a physiological and psychological insight into these important phenomena of the earliest cell-communities by observation and experiment on their modern representatives. Such permanent cell-communities or colonies are still found in great numbers both among the plasmodomous primitive plants (for instance, the paulotomacea, diatomacea, volvocinæ, etc.) and the plasmophagous primitive animals (the infusoria and rhizopods). In all these cœnobia we can easily distinguish two different grades of psychic activity: (1) the cell-soul of the individual cells (the “elementary organisms”) and (2) the communal soul of the entire colony.

III. The tissue-soul (histopsyche): third stage of phyletic psychogenesis.—In all multicellular, tissue-forming plants (metaphyta) and in the lowest, nerveless classes of tissue-forming animals (metazoa) we have to distinguish two different forms of psychic activity—namely: (1) the psyche of the individual cells which compose the tissue, and (2) the psyche of the tissue itself, or of the “cell-state” which is made up of the tissues. This “tissue-soul” is the higher psychological function which gives physiological individuality to the compound multicellular organism as a true “cell-commonwealth.” It controls all the separate “cell-souls” of the social cells—the mutually dependent “citizens” which constitute the community. This fundamental twofold character of the psyche in the metaphyta and the lower, nerveless metazoa is very important. It may be verified by unprejudiced observation and suitable experiment. In the first place, each single cell has its own sensation and movement, and, in addition, each tissue and each organ, composed of a number of homogeneous cells, has its special irritability and psychic unity (e.g., the pollen and stamens).

A. The plant-soul (phytopsyche) is, in our view, the summary of the entire psychic activity of the tissue-forming, multicellular plant (the metaphyton, as distinct from the unicellular protophyton); it is, however, the subject of the most diverse opinions even at the present day. It was once customary to draw an essential distinction between the plant and the animal, on the ground that the latter had a “soul” and the plant had none. However, an unprejudiced comparison of the irritability and movements of various higher plants and lower animals convinced many observers, even at the beginning of the century, that there must be a “soul” on both sides. At a later date Fechner, Leitgeb, and others strongly contended for the plant-soul. But a profounder knowledge of the subject was obtained when the similarity of the elementary structure of the plant and of the animal was proved by the cellular theory, and especially when the similarity of conduct of the active, living protoplasm in both was shown in the plasma theory of Max Schultze (1859). Modern comparative physiology has shown that the physiological attitude towards various stimuli (light, heat, electricity, gravity, friction, chemical action, etc.) of the “sensitive” portions of many plants and animals is exactly the same, and that the reflex movements which the stimuli elicit take place in precisely the same manner on both sides. Hence, if it was necessary to attribute this activity to a “soul” in the lower, nerveless metazoa (sponges, polyps, etc.), it was also necessary in the case of many (if not all) metaphyta, at least in the very sensitive mimosa, the “fly-traps” (dionaea and drosera), and the numerous kinds of climbing plants.