Here, as in sundry places throughout this chapter, the necessities of the argument have obliged me to forestall myself, by assuming the conclusion reached in a subsequent chapter, that modifications of structure produced by modifications of function are transmitted to offspring.
Whether the Volvox is to be classed as animal or vegetal is a matter of dispute; but its similarity to the blastula stage of many animals warrants the claim of the zoologists.
While the proof was in my hands there was published in Science Progress an essay by Dr. T. G. Brodie on "The Phosphorus-containing Substances of the Cell." In this essay it is pointed out that "nucleic acid is particularly characterized by its instability.... In the process of purification it is extremely liable to decompose, with the result that it loses a considerable part of its phosphorus. In the second place it is most easily split up in another manner in which it loses a considerable part of its nitrogen.... To avoid the latter source of error he [Miescher] found that it was necessary to keep the temperature of all solutions down to 0°C., the whole time of the preparation." These facts tend strongly to verify the hypothesis that the nucleus is a source of perpetual molecular disturbance—not a regulating centre but a stimulating centre.
The writing of the above section reminded me of certain allied views which I ventured to suggest nearly 50 years ago. They are contained in the Westminster Review for April, 1852, in an article entitled "A Theory of Population deduced from the General Law of Animal Fertility." It is there suggested that the "spermatozoon is essentially a neural element, and the ovum essentially a hæmal element," or, as otherwise stated, that the "sperm-cell is co-ordinating matter and the germ-cell matter to be co-ordinated" (pp. 490-493). And along with this proposition there is given some chemical evidence tending to support it. Now if, in place of "neural" and "hæmal," we say—the element that is most highly phosphorized and the element that is phosphorized in a much smaller degree; or if, in place of co-ordinating matter and matter to be co-ordinated, we say—the matter which initiates action and the matter which is made to act; there is disclosed a kinship between this early view and the view just set forth. In the last part of this work, "Laws of Multiplication," which is developed from the essay referred to, I left out the portion containing the quoted sentences, and the evidence supporting the conclusion drawn. Partly I omitted them because the speculation did not form an essential link in the general argument, and partly because I did not see how the suggested interpretation could hold of plants as well as of animals. If, however, the alleged greater staining capacity of the male generative nucleus in plants implies, as in other cases, that the male cell has a larger proportion of the phosphorized matter than the other elements concerned, then the difficulty disappears.
As, along with the idea just named, the dropped portion of the original essay contains other ideas which seem to me worth preserving, I have thought it as well to reproduce it, in company with the chief part of the general argument as at first sketched out. It will be found in Appendix A to this volume.
Unfortunately the word heterogenesis has been already used as a synonym for "spontaneous generation." Save by those few who believe in "spontaneous generation," however, little objection will be felt to using the word in a sense that seems much more appropriate. The meaning above given to it covers both Metagenesis and Parthenogenesis.