THE END.

FOOTNOTES:

[1] It seems needful here to say, that allusion is made in this paragraph to a proposition respecting the ultimate natures of Evolution and Dissolution, which is contained in an essay on The Classification of the Sciences, published in March, 1864. When the opportunity comes, I hope to make the definition there arrived at, the basis of a re-organization of the second part of First Principles: giving to that work a higher development, and a greater cohesion, than it at present possesses. [The intention here indicated was duly carried out in 1867.]

[2] Let me here refer those who are interested in this question, to Prof. Huxley’s criticism on the cell-doctrine, published in the Medico-Chirurgical Review in 1853.

A critic who thinks the above statements are “rather misleading” admits that the lowest types of organisms yield them support, saying that “there are certainly masses of protoplasm containing many nuclei, but no trace of cellular structure, in both animals and plants. Such non-cellular masses may exist during development and later become separated up into cells, but there are certain low organisms in which such masses exist in the adult state. They are called by some botanists non-cellular, by others multi-nucleate cells. Clearly the difference lies in the criteria of a cell. There are also some Protozoa, and the Bacteria, in which no nucleus has certainly been demonstrated. But it is usual to consider the bodies of such organisms as cells nevertheless, and it is supposed that such cells represent a stage of development in which the nucleus has not yet been evolved, though the chemical substance ‘nuclein’ has been formed in some of them.”

Perhaps it will be most correct to say that, excluding the minute, non-nucleated organisms, all the higher organisms—Metazoa and Metaphyta—are composed throughout of cells, or of tissues originally cellular, or of materials which have in the course of development been derived from cells. It must, however, be borne in mind that, according to sundry leading biologists, cells in the strict sense are not the immediate products either of the primitive fissions or of subsequent fissions; but that the multiplying so-called cells are nucleated masses of protoplasm which remain connected by strands of protoplasm, and which acquire limiting membranes by a secondary process. So that, in the view of Mr. Adam Sedgwick and others, the substance of an organism is in fact a continuous mass of vacuolated protoplasm.