phylogenetically in the idioplasm. At the same time the other adaptation determinants remain either undisturbed, or the new determinant is formed at the expense of related determinants which are already present and which may at last entirely vanish. Hence along with growing and complete determinants the idioplasm always contains likewise weakened and vanishing determinants. From the fact that a phylogenetic race is thrown repeatedly among different external conditions, it may at last unite in its idioplasm a large number of developing, mature, and vanishing adaptation determinants. This number is noticeably increased if in consequence of interbreeding a fusion of related idioplasms take place.

8. DEFINITE NOTIONS WITH REGARD TO THE MORPHOLOGY OF THE IDIOPLASM.

Since in the phylogenetic development of the plasma the thicker idioplasm is differentiated from the more fluid soma-plasm (§ 5), the former has the tendency by nature to assume a reticular arrangement. The strands of this network consist, in conformity with their origin, of parallel rows of micellæ extending lengthwise. These rows of micellæ are combined into more or less complex arrangements, so that the cross section of the strand represents the configuration of the idioplasm.[B]

Each ontogeny (individual) begins in a minute germ cell, in which a small quantity of idioplasm is contained. In the cell divisions, by which the organism grows, the idioplasm divides into as many parts as there are single cells, while it continually increases in quantity in a corresponding degree. The ontogenetic increase of the idioplasm takes place by length growth of the strands—that is, by intercalation of micellæ in each row of cells of the strands, which thereby grow in length without changing the configuration of the cross section.[C] Accordingly, each strand of idioplasm contains all the determinants that the particular individual has inherited in the germ cell, and each cell of the organism is idioplasmatically qualified to become the germ cell of a new individual. Whether this qualification may be realized depends upon the nature of the soma-plasm. In the lower plants this power belongs to each individual cell; in the higher plants many cells have lost it; in the animal kingdom it is possessed in general only by cells normally set apart as asexual or sexual reproductive cells.

The continued phylogenetic formation of the threads of idioplasm takes place by growth in the cross section, which contains the sum of all the determinants and changes in general only when new rows of micellæ are intercalated. But the rows of micellæ of the idioplasm join closely to each other, according to their thickness, so that only rarely new rows can enter, and then only at those definite places where the cohesion is less strong and hence is overcome. The cohesion varies irregularly because the configuration of the cross section, conformably to its origin, is never regular; the disruptive tensions are brought about by the unequal growth in length of the individual rows of micellæ. Dynamic influences have a decisive effect upon cohesion and disruptive tensions. The groups of micellæ of the configuration already obtained exercise these dynamic influences upon each other; and these dynamic influences can be modified by stimuli from without.

The idioplasm continually alters its configuration with its growth in successive ontogenies, but comparatively very slowly, so that it makes a minute advance from the germ of one generation to the germ of the next. The summation of these increments of advance through a whole line of evolution represents the race history of an organism, since the latter is connected only by its idioplasm in unbroken continuity with the micellar beginning of its race.

9. DEFINITE NOTIONS REGARDING THE FUNCTION OF THE IDIOPLASM.

A plasmic substance causes definite chemical and physical changes only when it is present in a certain condition of motion. The peculiar agency which the idioplasm has in each ontogenetic stage of development and in each part of the organism depends on the activity of a definite group of micellæ in the cross section of the strand or of a complex of such groups, while this local stimulus controls the chemical and physical processes by dynamic influence and by transmission of a specific mode of motion, even to a microscopically small distance.

The effective stimulus in a plasmic substance is dependent on its own nature and the influence which it receives from without. Which group of micellæ in the idioplasm receives the stimulus depends on the configuration, on the preceding stimuli and on the position in the individual organism in which the idioplasm is found. The determinants have arisen one after another during the whole period of evolution from the primordial cell. The configuration of the idioplasm is a character of phylogeny and the determinants in it have by nature the tendency to develop in the order in which they were formed. Further, since the ontogeny begins as a unicellular organism with the formation of a germ cell, that determinant of the idioplasm comes first to development, which has developed in the unicellular ancestor. Just so the succeeding stages of ontogeny depend for the time being on the development of the determinants having their origin in the corresponding stage of phylogeny. Both causes acting together—the phylogenetic configuration of the idioplasm and the successive morphological stages of development of the individual conditioned on it—necessarily result in the ontogeny being the repetition of the phylogeny.

If the whole remaining line of idioplasmic determinants in an ontogeny has reached development, the development of the germ-forming determinants finally follows as well from the configuration of the idioplasm as from the nature of the organism. The individual is capable of reproduction and the new ontogenies begin in the reproductive cells.

10. TRANSMISSION OF IDIOPLASMIC DETERMINANTS IN LOCAL VARIATION AND IN FECUNDATION.

The automatic progressive or perfecting transformation of the idioplasm is probably active in all stages of development, and proceeds regularly in all parts of the organism, because the idioplasm preserves its configuration at all times and places during the ontogeny. External stimuli impign upon the organism usually at a definite point, but they not only effect a local transformation of the idioplasm but also reproduce themselves in a dynamic manner in the entire idioplasm, which is in unbroken connection throughout the whole individual. The idioplasm is thus changed everywhere in the same manner, so that the germ cells that are given off at any point feel and inherit the effects of those local stimuli.

In the formation of the germ cells in sexual reproduction, the idioplasms of both parents must come into contact with each other, whereupon there results either a material union and formation of a mixed idioplasm or perhaps rather a dynamic action; and through these agencies there is produced a remodeled form which is, however, exactly equivalent to the combined idioplasms entering into it. Fertilization by diosmose of the spermatic substance is impossible.