ugh different stages (Hetero-epistase), which results in the
arrested development of certain characters in an organism, while others
progress and still others become retrogressive. As a rule use and
disuse are of great efficacy in this regard, and conjointly with these
compensation and correlation." Occasionally also irregular development
sets in, which proceeds by leaps.

Of course, Eimer could not but in his turn burn incense before Darwin
by declaring that he would not dare to cross swords with such a man,
while in reality he repudiates all of Darwin's fundamental tenets.

It may be well to state here in addition a few important supplementary
considerations: "Development can everywhere proceed in only a limited
number of directions because the constitution, the material composition
of the body, conditions these directions and prevents variation in all
directions." This is an important statement because Eimer clearly
expresses therein the difference between his own theory and that of
Naegeli. He makes the direction of development dependent on the
material composition of the body, whereas Naegeli considers it
dependent upon an internal tendency of every being to perfect itself,
hence upon a power inherent in the body. Eimer's view therefore tends
towards a mechanical explanation, while Naegeli postulates a vital
energy. The "internal causes" according to Eimer find their explanation
in the material composition of the body. Since the growth of the
individual organism depends on this composition and on the external
influences, Eimer compares family-development with it and designates
the latter as "organic growth." In opposition to Naegeli he maintains
that this "organic growth" does not always aim at perfection but often
tends to simplification and retrogression.

The following, then, according to Eimer, are the directive principles
of variation: (1). The general law of coloration (stripes running
lengthwise change into spots, stripes running crosswise change to a
uniform color). (2). The law of definitely directed local change (new
colors spread from the rear to the front and from above downward or
vice versa, old colors disappear in the same directions.) (3). The law
of male predominance (males are as a rule one step in advance of the
females in development). Female predominance is an exception. (4). The
law of age-predominance (new characters appear at a well-advanced age,
and at the time of greatest strength). (5).