following, the phylogenetic development consists solely in the continual progress of the idioplasm and the whole genealogical tree from the primordial drop of plasma up to the organism of the present day (plant or animal) is, strictly speaking, nothing else than an individual consisting of idioplasm, which at each ontogeny forms a new individual body, corresponding to its advance.

In this idioplasmic individual the automatic or perfecting variation is always active, so that the idioplasm of a phylogenetic line always grows by propagation of the determinants contained within it, as a tree grows larger through its whole duration of life by branching. On the other hand the adaptation variation caused by external stimuli is present only in those periods of the phylogenetic line in which the idioplasm, and together with this the individual, do not possess the obtainable maximum of adaptation to their environment for the time being. Both of these variations of the idioplasm take place so slowly that only after a long series of generations do the new determinants become capable of developing and revealing themselves in the transmutation of visible characters.

Aside from the phylogenetic variations already named, which take place according to the measure of ontogenetic growth, the idioplasm undergoes, as a result of crossing, as well as in changes of the ontogeny, gamogenic variations which may be designated as stationary, since in the mingling of sexually different idioplasms there arise only new arrangements of determinants already present, but no new formation of determinants takes place. Hence in this way arise also new combinations of developmental characteristics.

As a result of external injurious influences, abnormal variations, or pathological variations, appear in the idioplasm. These consist of disturbances of equilibrium, which take place also without new formation of determinants. Thereby the determinants already present are caused to develop in abnormal relations, and mostly in reversions.

Apart from the inheritable variations of the idioplasm just enumerated, and the transformations of visible characters involved in it, the soma-plasm and the non-plasmic substances experience, by the influence of nutrition and climate, greater or less variations, which constitute nutrition varieties, and since the idioplasm remains unaffected in general, last only so long as the causes which called them forth.[F]

If we have in mind the inner nature of the organism, there is, properly speaking, no such specific phenomenon as heredity, since the phylogenetic line is a continuous idioplasmic individual. In this sense heredity is nothing more than the persistence of organized substance in a movement in which variations are automatically induced, or the necessary transition of one idioplasmic configuration into the next following. It is present, not only among plant and animal individuals which are ontogenetically separated, but also everywhere within these individuals, where individual parts (cells, organs) follow each other in time. Hereditary phenomena are those that necessarily pass over to following generations, and in general those that are located in the idioplasm, since non-idioplasmic substance can be hereditary only through a limited number of cell generations.

Variations and heredity are generally estimated, not according to the inner nature of the mature individuals, but according to their relation in successive generations, since heredity is assumed when the ontogenetic characters remain the same, and variation when previously latent characters become visible. But these phenomena belong to another department of science; they concern the possibility and reality of development of the idioplasmic determinants.

17. VARIETY, RACE, MODIFICATION.

From the multifarious variations of organisms proceed various categories of kinship. Varieties arise by extremely slow changes in the idioplasm due to the perfecting process and adaptation. Since these are conditioned by the same causes, they follow in all individuals of the same variety in uniform manner. Varieties are uniform, entirely constant under the most various external conditions, in general cross only with difficulty with related varieties, are not varied by accidental crosses, and persist through geological periods. Varieties belong to feral nature rather than to culture; they can assume all possible modifications without injury to their specific characteristics, but can show no distinctions of races, for all beginnings of race formation are destroyed by free intercrossing. They differ from species only in that they are to be designated as more closely related species, or species as more remotely related varieties. Every other distinguishing characteristic is wanting.

Races arise from gamogenic or pathological variations of the idioplasm. In the former case they presuppose crossing between related varieties or species, in the latter case an increased sensibility and weakening of the idioplasm. Very often both causes co-operate, since crossing follows more easily when the idioplasm is weakened by hurtful influences and since the irritability and weakening of the idioplasm increases if crossing has preceded. Race formation begins in single individuals. Among several individuals it begins in various directions because the causes are different and hence may display a great multiformity. Races are distinguished by more or less abnormal characteristics; they arise quickly—often in a single generation—and present various degrees of stability. This stability is insured to some extent only by the strictest in-and-in breeding. All races disappear through crossing, likewise many races that have arisen from pathological variations disappear even in sexual reproduction (in self-fecundation). Races belong exclusively to cultivation, where they can develop and exist protected from free intercrossing.

While varieties and races arise by progressional or stationary variation of the idioplasm, modifications are produced by such influences of nutrition and climate as act only on the soma-plasm and the non-plasmic substances, and hence do not give rise to inheritable characters in the organism. Modifications persist only so long as their causes, and under other environments immediately pass over into the modifications corresponding to them. The transition is completed in the lowest plants during a limited number of cell generations; in an individual of the higher plants on the same stem during the growth of a single year. Each variety and each race appears clothed in a definite modification, and can change it within a range peculiar to itself.[G]

18. SOCIAL AND INDIVIDUAL ORIGIN OF SPECIES.

The species arises neither from the nutrition variety nor from the race; it is always a more advanced variety, and hence species formation is identical with variety formation. Cause for variation and consequently for variety formation is always shown, either when, environment remaining the same, the automatic variation of the idioplasm has advanced so far that the ontogeny is raised to a higher grade of organization and division of labor, or when external stimuli act for a sufficiently long time in a manner not in harmony with