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Updated: May 18, 2025
The position taken must be this: Though mucous membrane in a highly-evolved individual organism, thus shows the powerful effect of the medium on its surface; yet we must not suppose that the medium had the effect of producing such a cell-structure on the surfaces of primitive forms, undifferentiated though they were; or, if we suppose that such an effect was produced on them, we must not suppose that it was inheritable.
I thought: Here am I, capable of teaching him much concerning the field wherein he labours the nitrogenic why of the fertilizer, the alchemy of the sun, the microscopic cell-structure of the plant, the cryptic chemistry of root and runner but thereat he straightened his work-wearied back and rested. His eyes wandered over what he had produced in the sweat of his brow, then on to mine.
And now we have a perfect cell-structure, differing from an ordinary cell only in having the inner sac, inclosing the dot, on the side, instead of in the centre. The outer membrane corresponds to the Ectoblast, or outer cell sac, the Purkinjean vesicle to the Mesoblast, or inner cell sac, while the dot in the centre answers to the Entoblast.
The operation of those forces which produced the primary differentiation of outer from inner in early minute masses of protoplasm, pre-determined this universal cell-structure of all embryos, plant and animal, and the consequent cell-composition of adult forms arising from them.
Suppose, for instance, we say that the structure of the epidermis is wholly determined by the natural selection of favourable variations; what must be the position taken in presence of the fact above named, that when mucous membrane is exposed to the air its cell-structure changes into the cell-structure of skin?
But while we recognize the identity of cell-structure and egg-structure at this point in the history of the egg, we must not forget the great distinction between them, namely, that, while the cells remain component parts of the whole body, the egg separates itself and assumes a distinct individual existence.
Haeckel’s demonstration of the possibility of spontaneous generation is along these lines. He refers to the cytodes, the blood corpuscles, to alleged or actual non-nucleated cells, to bacteria, to the simplest forms of cell-structure, as proofs of the possibility of a descending series of connecting-links. Unfortunately, this primitive slime soon proved itself an illusion.
As the title suggests, the main idea that actuated Schwann was to unify vegetable and animal tissues. Accepting cell-structure as the basis of all vegetable tissues, he sought to show that the same is true of animal tissues, all the seeming diversities of fibre being but the alteration and development of what were originally simple cells.
In many fragments the cell-structure of the wood is still visible, but in others nature has carried the process further, and crystallization has transformed the wood of these old, old trees into the brilliant fragments we can have for the carrying "beautiful wood replaced by beautiful stone," as Mr. Muir was fond of saying.
The farmer has no longer Indians to fight or a wilderness to subdue, but the soils of his farm are analyzed at his state university by men who live in the daily atmosphere of the romance of science, and who say, as a professor in the University of Chicago said once, that "a flower is so wonderful that if you knew what was going on within its cell-structure, you would be afraid to stay alone with it in the dark."
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