Herbert Spencer

“ Hence, then, there is congruity between the above interpretation and certain general truths displayed by animal organization at large. We may infer that in a way parallel to that just indicated, cell-evolution was, under one of its aspects, a change from a stage in which the exciting substance and the substance excited were mingled with approximate uniformity, to a stage in which the exciting substance was gathered together into the nucleus and finally into the chromosomes: leaving behind the substance excited, now distinguished as cytoplasm. ”

“ In the sperm-cell there occurs just that failure in the production of chromatin which, according to the hypothesis above sketched out, is to be expected; for, in the process of cell-multiplication, the cells which become spermatozoa are left with half the number of chromosomes possessed by preceding cells: there is actually that impoverishment and declining vigour here suggested as the antecedent of fertilization. It needs only to imagine the ovum and the polar body to be alike in size, to see the parallelism ”

“ Concerning the protoplasm contained in each cell, named by some cytoplasm, it remains to say that it always includes a small body called the centrosome, which appears to have a directive function. Usually the centrosome lies outside the nucleus, but is alleged to be sometimes within it. ”

“ When the time for fission is approaching this dispersed chromatin begins to gather itself together: reaching its eventual concentration through several stages. By its concentration are produced the chromosomes, constant in number in each species of plant or animal. It is alleged that the substance of the chromosomes is not continuous, but consists of separate elements or granules, which have been named chromomeres ”

“ Conjugation among the Protophyta and Protozoa, beginning with cases in which there is a mingling of the contents of two cells in no visible respect different from one another, and developing into a great variety of processes in which they differ, must be left aside, and attention limited to the terminal process of fertilization as displayed in higher types of organisms. ”

“ A concomitant truth, or the same truth under another aspect, is that Nature everywhere presents us with complexities within complexities, which go on revealing themselves as we investigate smaller and smaller objects. In a preceding chapter ( §§ 54a, 54b) it was pointed out that each primitive organism, in common with each of the units out of which the higher and larger organisms are built, was found a generation ago to consist of nucleus, protoplasm, and cell-wall. This general conception of a cell remained for a time the outcome of inquiry ”

“ It was there pointed out that in animal organisms the various structures are so arranged that evolution of a small amount of energy in one, sets up evolution of a larger amount of energy in another; and often this multiplied energy undergoes a second multiplication of like kind. ”

“ The effect of subdivision in producing a large area in a small space, is shown in the lungs, where the air-cells on the sides of which the blood-vessels ramify, are less than 1⁄100th of an inch in diameter, while they number 700,000,000. In the composition of every tissue we see the same principle. The living part, or protoplasm, is divided into innumerable protoplasts, among which are distributed the materials and agencies producing changes. And now we find this principle carried still deeper in the structure of the protoplasm itself. ”

“ Speculation aside, however, we may say that the two functions of the chromatin do not exclude one another, but that the general activity which originates from it may be but a lower phase of that special activity caused by fertilization. [2]
§ 74g. Here we come unawares to the remaining topic embraced under the title Cell-Life and Cell-Multiplication. We pass naturally from asexual multiplication of cells to sexual multiplication—from cell-reproduction to cell-generation. The phenomena are so numerous and so varied that a large part of them must be passed over. ”

“ If a protozoon, the weaker progeny arising by division of it will originate an inferior stirp, unable to compete successfully with that arising from the sister-cell endowed with a larger portion of chromatin. By continual elimination of the varieties which produce unequal halving, necessarily at a disadvantage if a moiety of their members tend continually to disappear, there will be established a variety in which the halving is exact: the character of this variety being such that all its members aid the permanent multiplication of the species. ”

“ What is the nature of the coercion exercised by the centrosome—a body hardly distinguishable in size from the microsomes or granules of protoplasm around—is not known. It can scarcely be a repelling force ”

“ Anyone who drops into dilute sulphuric acid a small nail and then drops a pinch of iron filings, will be shown, by the rapid disappearance of the last and the long continuance of the first, how greatly the increasing of surfaces by multiplication of fragments facilitates change. ”

“ All higher types exhibit this differentiation. Be it muscle or gland or other operating organ, the cause of its activity lies not in itself but in a nervous agent, local or central, with which it is connected. ”

“ That a tractive force is at work seems inferable from the results. For the separated halves of the split chromosomes, which now form clusters on the two sides of the equatorial plane, gradually part company, and are apparently drawn as clusters towards the opposing centrosomes. ”