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If plants and animals all developed from a one-celled animal, such as the amoeba, why did not the amoeba develop? Or, if some developed, why not all? Certainly there would not remain a great multitude of species in the microscopic world. Of many species small and large, we have many fossils preserved but no transitional forms.
We do not know, it is said, by what means the structureless viscid substance which we call protoplasm can build for itself a solid bone; we do not understand how an amoeba makes its test; no one understands how anything is done unless he can do it himself; and even then he probably does not know how he has done it.
Amoeba, like every other living thing, if it is to exist, must unconsciously obey the first great commandment of nature, "Preserve thyself." But its life is incomplete if it stops with the furtherance of aims that we may call purely selfish. Nature also demands that an Amoeba, again like every other living thing, shall perpetuate its kind.
If you can turn a pedestrian into a cyclist, and a cyclist into a pianist or violinist, without the intervention of Circumstantial Selection, you can turn an amoeba into a man, or a man into a superman, without it.
The slightest movement of the thin cover-glass placed over the drop of water in which an amoeba is immersed, on a microscopic slide, suffices to act as a stimulus, and serves much the same purpose as an electric shock to the muscles of a man.
It may therefore be useful to consider one or two intermediate forms and the parallel embryonic stages of higher animals, and to see how the higher many-celled animal originates from the unicellular stage. The amoeba is an illustration of a great kingdom of similar, practically unicellular forms, which have played no unimportant part in the geological history of the globe. These are the protozoa.
Your amoeba or vorticella, as the case may be, splits in two. Then there are two amoebæ or vorticellæ. In this way the necessity of the family, that middle-class institution so abhorrent to the artistic mind, is avoided. In my friend's drop of ditch-water, as in heaven, there is neither marrying nor giving in marriage.
Its depths conceal every kind of subtlety and sophistication, high endeavour, and a response to beauty and wisdom of a sort far removed from the amoeba stage of development above sketched.
No comment will, one would think, be necessary to make the reader feel that the difference between the terebella and the amoeba is one of degree rather than kind, and that if the action of the second is as conscious and reasonable as that, we will say, of a bird making her nest, the action of the first should be so also.
It is impossible to derive Metazoa from Protozoa in their present finished state of evolution; even the Amoeba is so exactly adapted in organisation and functional activity to the conditions of its existence that it is a “finished” type. It is only by a stretch of fancy that fishes can be derived from worms, or higher vertebrates from fishes.
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