Even the latest theory, developed especially by Ludwig in Germany—that protoplasm contains a separate enzyme for each separate function appointed to a particular task—amounts to nothing more than an analysis of the living organism.
The Formation of Multicellular Organisms
We cannot say that the cell is the element of life, because, in an absolute sense, it is not alive; it lives only when it constitutes an individual. Even the brain cells, the muscular fibres, the leucocytes, etc., are cells; but they do not live independently; their life depends upon the living individual that contains them. We may, however, define the cell as the means, the morphological material, out of which all living organisms are formed: because, from the algæ to the orchids, from the cœlenterata up to man, all complex organisms are composed of an accumulation of those microscopic little bodies that we call cells.
The manner of union between the cells in the most primitive living colonies, whether vegetable or animal, is analogous to that followed in the segmentation of the ovum in its ontogenetic (i.e., individual) development.
But the manner of construction differs notably, as between animal and vegetable cells.
Vegetable cells, on the one hand, have a resistant and strongly protective membrane; animal cells, on the contrary, have either a very thin membrane or none at all. Vegetable cells, as though made venturesome by their natural protection, proceed to invade their environment in colonies—in other words, the cells dispose themselves in series of linear ramifications—witness the formation of primitive algæ; and analogously the expansion of the higher types of vegetation into their environment, with branches, leaves, etc. And just as though the vegetable cell acquired self-confidence because it is so well protected, it becomes stationary and strikes its roots into the soil.
To this same fact of cellular protection must be attributed the inferior sensibility and hence the permanent state of obscured consciousness in vegetable life.
This protection against the assaults of environment, and the consequent lack of sensibility, constitute from the outset an inferior stage of evolution.
Animal cells have an entirely different manner of forming themselves into colonies; acting as though they were afraid, they group themselves in the form of a little sphere, enclosing their environment within themselves, instead of reaching out to invade it; and subsequent developments of the animal cell consist in successive and complex invaginations, or formations of layers, one within another—instead of ramifications, after the manner of vegetable cells.