If heredity and variation are defined according to the true nature of
organisms, they are only apparent opposites. Since idioplasm alone is
transmitted from one ontogeny to the next 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 climat