Every part, or the whole, of the Moneron absorbs food and oxygen—it is all mouth and lungs. Every part, or the whole, digests the food—it is all stomach. Every part, or the whole, performs the reproductive function—it is all reproductive organism. Every part of it senses the impressions from outside, and responds to it—it is all organs of sense, and organs of motion. It envelops its prey as a drop of glue surrounds a particle of sand, and then absorbs the substance of the prey into its own substance. It moves by prolonging any part of itself outward in a sort of tail-like appendage, which it uses as a "foot," or "finger" with which to propel itself; draw itself to, or push itself away from an object. This prolongation is called a pseudopod, or "false-foot." When it gets through using the "false-foot" for the particular purpose, it simply draws back into itself that portion which had been protruded for the purpose.
It performs the functions of digestion, assimilation, elimination, etc., perfectly, just as the higher forms of life—but it has no organs for the functions, and performs them severally, and collectively with any, or all parts of its body. What the higher animals perform with intricate organs and parts—heart, stomach, lungs, liver, kidneys, etc., etc.—this tiny creature performs without organs, and with its entire body, or any part thereof. The function of reproduction is startlingly simple in the case of the Moneron. It simply divides itself in two parts, and that is all there is to it. There is no male or female sex in its case—it combines both within itself. The reproductive process is even far more simple than the "budding" of plants. You may turn one of these wonderful creatures inside out, and still it goes on the even tenor of its way, in no manner disturbed or affected. It is simply a "living drop of glue," which eats, digests, receives impressions and responds thereto, and reproduces itself. This tiny glue-drop performs virtually the same life functions as do the higher complex forms of living things. Which is the greater "miracle"—the Moneron or Man?
A slight step upward from the Moneron brings us to the Amoeba. The name of this new creature is derived from the Greek word meaning "change," and has been bestowed because the creature is constantly changing its shape. This continual change of shape is caused by a continuous prolongation and drawing-in of its pseudopods, or "false-feet," which also gives the creature the appearance of a "many-fingered" organism. This creature shows the first step toward "parts," for it has something like a membrane or "skin" at its surface, and a "nucleus" at its centre, and also an expanding and contracting cavity within its substance, which it uses for holding, digesting and distributing its food, and also for storing and distributing its oxygen—an elementary combination of stomach and lungs! So you see that the amoeba has taken a step upward from the moneron, and is beginning to appreciate the convenience of parts and organs. It is interesting to note, in this connection, that while the ordinary cells of the higher animal body resemble the monera in many ways, still the white corpuscles in the blood of man and the animals bear a startling resemblance to the amoebae so far as regards size, general structure, and movements, and are in fact known to Science as "amoeboids." The white corpuscles change their shape, take in food in an intelligent manner, and live a comparatively independent life, their movements showing independent "thought" and "will."
Some of the amoebae (the diatoms, for instance) secrete solid matter from the water, and build therefrom shells or houses, which serve to protect them from their enemies. These shells are full of tiny holes, through which the pseudopods are extended in their search for food, and for purposes of movement. Some of these shells are composed of secreted lime, and others of a flinty substance, the "selection" of these substances from the ether mineral particles in the water, evidencing a degree cf "thought," and mind, even in these lowly creatures. The skeletons of these tiny creatures form vast deposits of chalk and similar substances.
Next higher in the scale are the Infusoria. These creatures differ from the amoebae inasmuch as instead of pseudopods, they have developed tiny vibrating filaments, or thread-like appendages, which are used for drawing in their prey and for moving about. These filaments are permanent, and are not temporary like the pseudopods of the monera or amoebae—they are the first signs of permanent hands and feet. These creatures have also discovered the possibilities of organs and parts, to a still greater degree than have their cousins the amoebae, and have evolved something like a mouth-opening (very rudimentary) and also a short gullet through which they pass their food and oxygen—they have developed the first signs of a throat, wind-pipe and food-passage.
Next come the family of Sponges, the soft skeletons of which form the useful article of everyday use. There are many forms who weave a home of far more delicacy and beauty than their more familiar and homely brothers. The sponge creature itself is a slimy, soft creature, which fills in the spaces in its spongy skeleton. It is fastened to one spot, and gathers in its food from the water around it (and oxygen as well), by means of numerous whip-like filaments called cilia, which flash through the water driving in the food and oxygen to the inner positions of its body. The water thus drawn in, as well as the refuse from the food, is then driven out in the same manner. It is interesting to note that in the organisms of the higher animals, including man, there are numerous cilia performing offices in connection with nutrition, etc. When Nature perfects an instrument, it is very apt to retain it, even in the higher forms, although in the latter its importance may be dwarfed by higher ones.
The next step in the ascending scale of life-forms is occupied by the polyps, which are found in water, fastened to floating matter. The polyps fasten themselves to this floating matter, with their mouths downward, from the latter dangling certain tentacles, or thin, long arms. These tentacles contain small thread-like coils in contact with a poisonous fluid, and enclosed in a cell. When the tentacles come in contact with the prey of the creature, or with anything that is sensed as a possible enemy, they contract around the object and the little cells burst and the tiny thread-like coils are released and twist themselves like a loop around the object, poisoning it with the secreted fluid. Some of the polyps secrete flint-like tubes, which they inhabit, and from the ends of which they emerge like flowers. From these parent polyps emerge clusters of young, resembling buds. These bud-like young afterwards become what are known as jelly-fishes, etc., which in turn reproduce themselves—but here is a wonder—the jelly-fish lay eggs, which when hatched produce stationary polyps like their grandparent, and not moving creatures like their parents. The jelly-fishes have a comparatively complex organism. They have an intricate system of canal-like passages with which to convey their food and oxygen to the various parts. They also have something like muscles, which contract and enable the creature to "swim." They also possess a "nervous system," and, most wonderful of all, they have rudimentary eyes and ears. Their tentacles, like those of the parent-polyp, secrete the poisonous fluid which is discharged into prey or enemy.
Akin to the polyps are the sea-anemones, with their beautiful colors, and still more complex structure and organism, the tentacles of which resemble the petals of a flower. Varying slightly from these are the coral-creatures, which form in colonies and the skeletons of which form the coral trees and branches, and other forms, with which we are familiar.
Passing on to the next highest family of life-forms, we see the spiny-bodied sea-creatures, such as the sea-urchin, star-fish, etc., which possess a thick, hard skin, covered by spines or prickly projections. These creatures abound in numerous species. The star-fish has rays projecting from a common centre, which gives it its name, while the sea-urchin resembles a ball. The sea-lilies, with their stems and flowers (so-called) belong to this family, as do also the sea-cucumbers, whose name is obtained from their shape and general appearance, but which are animals possessing a comparatively complex organism, one of the features of which is a stomach which may be discarded at will and replaced by a new one. These creatures have a well defined nervous system, and have eyes, and some of them even rudimentary eyelids.
Ascending the scale of life-forms, we next observe the great family of the Annulosa, or jointed creatures, which comprises the various families of the worm, the crab, the spider, the ant, etc. In this great family are grouped nearly four-fifths of the known life-forms. Their bodies are well formed and they have nervous systems running along the body and consisting of two thin threads, knotted at different points into ganglia or masses of nerve cells similar to those possessed by the higher animals. They possess eyes and other sense organs, in some cases highly developed. They possess organs, corresponding to the heart, and have a well-developed digestive apparatus. Note this advance in the nutritive organism: the moneron takes its food at any point of its body; the amoeba takes its food by means of its "false-feet," and drives it through its body by a rhythmic movement of its substance; the polyp distributes its food to its various parts by means of the water which it absorbs with the food; the sea-urchin and star-fish distribute their food by canals in their bodies which open directly into the water; in the higher forms of the annulosa, the food is distributed by a fluid resembling blood, which carries the nourishment to every part and organ, and which carries away the waste matter, the blood being propelled through the body by a rudimentary heart. The oxygen is distributed by each of these forms in a corresponding way, the higher forms having rudimentary lungs and respiratory organs. Step by step the life-forms are perfected, and the organs necessary to perform certain definite functions are evolved from rudimentary to perfected forms.