2. During this continuous life the idioplasm goes through a development of its own, just as an individual organism goes through a certain cycle of development during its individual life. This development consists in a constantly increasing complexity of structure and differentiation of function.
3. This development is automatic, resulting from internal forces or movements, (Vervollkommnungs-bewegungen).
4. As a result of the increasing complexity of structure in the idioplasm the entire organism, which in each generation rearises therefrom, becomes, from generation to generation, more and more complex with greater and greater differentiation of function. Thus the progression of the idioplasm controls the phylogeny of the race. It marks out the course of evolution.
5. Since, according to Nägeli, new life with new idioplasms, may arise wherever and whenever the necessary conditions combine, the present organic world is not made up from branchings of a single original idioplasm, but each race or group may have its own specific idioplasm; and, since this has its own characteristic structure and its own specific internal perfecting forces, it passes through its own peculiar evolution, carrying with it its own depending race of organisms.
The fact that animals and plants at the present time show such various degrees of organization is also accounted for on the last supposition, for those of lowlier organization are merely of more recent origin and have not progressed so far in idioplasmic development.
This automatic perfecting principle has been the mark of much criticism. Some have confounded it with the mystical nisus formativus, or formative principle of preceding theorists. But, as Weismann remarks, Nägeli's phyletic force is conceived as a thoroughly scientific mechanical principle. Nägeli has simply made application in the organic world of the principle of entropy, as stated in the mechanical theory of heat. Nägeli himself also compares his internal perfecting principle to mechanical inertia. He says, "the force of evolution once started in a given direction, tends to continue in the same direction. This constitutes the law of inertia in the organic world."
Two other matters remain to be noticed. The first of these is Nägeli's use of the German word Anlage. We have been unable to give a perfectly satisfactory translation of this word in its technical meaning. We have received some comfort, though but little help, from the experience of the translators of similar works. Selmar Schoenland, in translating from Weismann, renders it variously as "germ," "germ of structure," "germ (of Nägeli)," "germ of Nägeli," "Nägeli's preformed germ of structure," "preformed germs," "tendency." Another translator renders the word as "constitutional element." The translation, "determinant," which we have selected is an appropriation of an analogous but not absolutely identical technical term from Weismann's Germinal Selection. The use of the word in this connection is open to the objection that it has previously been used technically for a somewhat different idea by another author. M. C. Potter, in his translation of Warming's Systematic Botany, following Dr. E. L. Mark, renders the word Anlage as "fundament." Dr. H. C. Porter, in his translation of the Bonn Text-Book of Botany, renders the same word as "rudiment."
In general the word Anlage means beginning, plan, disposition to anything, and hence involves the ideas of origin, organization and tendency. Sanders defines the word in one of its meanings as: "The act of planning or beginning anything; the act of laying the foundation of any work intended to be carried on toward completion, in order that from the beginning made, a definite thing may be developed or may develop itself"; (i.e., to determine, in the sense of limiting to a particular purpose or direction, hence determinant). "Also, the thing begun or planned, considered as the basis and germ of the further development of that which has already originated."
In its restricted use as applied to organisms it would mean "germ," in the sense of embryonic starting point. More specifically, it is a portion of plastic, organized substance, functioning as an individual and containing potentially an elemental organ plus a formative power. In Nägeli's own words, "There exists an essential difference between the substance of a mature organism which does not possess the capability of further development, and the substance of an egg, which does possess this capability. By virtue of this difference the egg-substance is characterized as the Anlage, or germ of the mature organism. All characteristics of the adult condition are potentially contained in the ovum."