tion to the heavenly bodies. Naegeli has applied this law to
molecules, unsupported, however, by any evidence other than that of
analogy. On the other hand, there is evidence that molecules do not
invariably act according to this law.

Spontaneous generation (p. 4) was an important item in Naegeli's
doctrine, and might almost be said to be fundamental to it, although it
is not really necessary to the internal perfecting principle, which may
be regarded as the chief feature of the Mechanico-Physiological Theory.
Up to 1865 Naegeli believed in the spontaneous origin of many fungi, and
thought that it could be demonstrated. He was obliged to abandon the
experimental evidence, but to the close of his life held the views of
abiogenesis presented in the accompanying translation.

The characteristic and most interesting feature of the
Mechanico-Physiological Theory is certainly Naegeli's conception of an
automatic perfecting principle (_Autonome Vervollkommnung_). This
conception may be briefly outlined as follows:

1. The essential part of the reproductive plasm, termed idioplasm, since
it divides and passes over from generation to generation, in higher as
well as in lower organisms, has a continuous or "immortal" existence.[I]

[I] Naegeli's idioplasm corresponds in many respects, though by
no means in all, to Weismann's germ-plasm. Weismann's idea of
continuity or "immortality," which has been so widely noticed,
is set forth with equal clearness, though with less emphasis, by
Naegeli.

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 Naegeli, new life with new idioplasms, may arise
wherever and whenever the necessary conditions combine, the present
organi