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Updated: June 24, 2025
The graceful Diatom is a morsel of plasm enclosed in a flinty box, often with a very pretty arrangement of the pores and markings. The Desmid has a coat of cellulose, and a less graceful coat of cellulose encloses the Peridinean. Then the social principle enters. First we have loose associations of one-celled plants in a common bed, then closer clusters or many-celled bodies.
One step higher in the scale stands the plant-form called Volvox, near the border-line between the one-celled and the many-celled organisms. This aquatic type, about the size of the head of an ordinary pin, is a hollow spherical colony, with a wall composed of closely set cellular components.
Examine it first in its natural condition, and then after soaking for an hour or two in a solution of carmine. Make drawings. Mount on a glass slide some of the scum found on stagnant water and examine it with a compound microscope. The forms most frequently seen by such an examination are one-celled plants. Many of these have the power of motion.
The social tendency which pervades the animal world, and the evident use of that tendency, prepare us to understand that the primitive microbes would naturally come in time to live in clusters. Union means effectiveness in many ways, even when it does not mean strength. We have still many loose associations of one-celled animals in nature, illustrating the approach to a community life.
It is a long distance from the mechanical activities of the protozoön to the processes of human thought; yet the physical basis of the latter is a cellular mechanism and nothing more, developed during a single human life in company with all other organs from a one-celled starting-point the human egg.
Of the muscle-cell, the liver-cell, and the one-celled animal we may affirm the same properties, but the difference is that while all are secretory the liver-cell is eminently so, and produces bile, which other cells do not; that while it is but feebly contractile, or susceptible of change of form, the muscle-cell is characterized by this property above all others.
We are asked to believe that some plants became animals, or some animals became plants, or that all plants and animals came from the one germ they allowed God to create. They say that all species developed by growth, but do not explain why we still have the one-celled amoeba, the microscopic bacilli of plant life, and the microscopic species of animal life.
However that may be, the Sponges soon begin to absorb the silica or lime of the sea-water, and deposit it in needles or fragments in their bed. The deposit goes on until at last an elaborate framework of thorny, or limy, or flinty material is constructed by the one-celled citizens.
In the new southern ocean another branch of these Thalamophores, the Nummulites, spreads with such portentous abundance that its shells sometimes alone, generally with other material make beds of solid limestone several thousand feet in thickness. The pyramids are built of this nummulitic limestone. The one-celled animal in its shell is, however, no longer a microscopic grain.
But even a single cell lends itself to infinite variety of shape, and we have to penetrate to the very lowest level of this luxuriant world of one-celled organisms to obtain some idea of the most primitive living things. Properly speaking, there were no "first living things."
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