are destined to give the future direction
to biology, they will in a measure only be bringing biology back to its
pre-materialistic tradition, the tradition of Aristotle, Cuvier, von
Baer and J. Mueller. It may well be that the intransigent materialism of
the 19th century is merely an episode, an aberration rather, in the
history of biology--an aberration brought about by the over-rapid
development of a materialistic and luxurious civilisation, in which
man's material means have outrun his mental and moral growth.

Two movements seem significant in the morphology of the last decade or
so of the 19th century--first, the experimental study of form, and
second, the criticism of the concepts or prejudices of evolutionary
morphology.

The period was characterised also by the great interest taken in
cytology, following upon the pioneer work of Hertwig, van Beneden and
others on the behaviour of the nuclei in fertilisation and
maturation.[519] This line of work gained added importance in connection
with contemporary research and speculation on the nature of hereditary
transmission, and it has in quite recent years received an additional
stimulus from the re-discovery of Mendelian inheritance. Its importance,
however, seems to lie rather in its possible relation to the problems of
heredity than in any meaning it may have for the problems of form. More
significant is the revolt against the cell-theory started by Sedgwick[520]
and Whitman,[521] on the ground that the organism is something more than
an aggregation of discrete, self-centred cells.

The experimental work on the causes of the production and restoration of
form infused new life into morphology. It opened men's eyes to the fact
that the developing organism is very much a living, active, responsive
thing, quite capable of relinquishing at need the beaten track of normal
development which its ancestors have followed for countless generations,
in order to meet emergencies with an immediate and purposive reaction.
It was cases of this kind, cases of active regulation in development and
regeneration, that led men like G. Wolff and H. Driesch to cast off the
bonds of dogmatic Darwinism and declare boldly for vitalism and
teleology.

There was the famous case of the regeneration of the lens in Amphibia
from the edge of the iris--an entirely novel mode of origin, not
occurring in ontogeny. The fact seems to have been discovered first by
Colucci in 1891, and independently