luences due to external causes (St. Hilaire), and to use and disuse of
organs (Lamarck). These influences affect the structure of the gemmaria,
and as the germ-cells consist of gemmaria, like those of the rest of the
organism, the possibility of the transmission of acquired new characters
is self-evident. The importance of correlated growth and orthogenesis is
explained on a similar basis, and the Darwinian conceptions of the
independent variation of individual parts, of the exclusive dominance of
utility, of the influence of the struggle for existence in regard to
individual selection, and of the omnipotence of natural selection, are
energetically denied.

Oscar Hertwig,(68) de Vries, Driesch(69) and others attempt to reconcile
the preformationist and the epigenetic standpoints, and "to extract what
is good and usable out of both." Hertwig and Driesch, however, can only be
mentioned with reservations in this connection.

We cannot better sum up the whole tendency of the construction of
mechanical theories on these last lines than in the words of Schwann:
"There is within the organism no fundamental force working according to a
definite idea; it arises in obedience to the blind laws of necessity."

So much for the different lines followed by the mechanical theories of
to-day. An idea of their general tenor can be gained from a series of much
quoted general treatises, of which we must mention at least the
"classics." In Wagner's "Handwoerterbuch der Physiologie," 1842, Vol. I.,
Lotze wrote a long introductory article to the whole work, on "Life and
Vital Force." It was the challenge of the newer views to the previously
vitalistic standpoint, and at the same time it was based on Lotze's
general principles and interspersed with philosophical criticism of the
concepts of force, cause, effect, law, &c.(70) A similar train of ideas to
Lotze's is followed to-day by O. Hertwig, especially in his "Mechanismus
und Biologie."(71) Lighter and more elegant was the polemic against vital
force, and the outline of a mechanical theory which Du Bois-Reymond
prefaced to his great work, "Untersuchungen ueber die tierische
Electricitaet" (1849). It did not go nearly so deep as Lotze's essay, but
perhaps for that very reason its phrases and epigrams soon became common
property. We may recall how he speaks of vital force as a "general servant
for everybody," of the iron atom which remains the same whether it be in
the meteorite in cosmic spa