f the principle of natural
selection to show how these characters conduced to the preservation and
further evolution of the species. And out of this interest in the theory
of natural selection grew in the last twenty years of the nineteenth
century the greatly increased attention to the facts and theories of
heredity, which was stimulated by Darwin's hypothesis of Pangenesis and
especially by Weismann's speculations about the nature and behaviour of
the 'germ-plasm'. Before the appearance of Weismann's work, the
germ-cells, which bear somehow or other the hereditary characters that
appear in the offspring, were supposed to be produced directly from the
body of the parent. Darwin provisionally suggested that every cell of
every organism gives off minute particles which become congregated in
the germ-cells, and that these cells thus contain representative
portions of all parts of the parent's body. Weismann, on the basis of
his work on the origin of the germ-cells in Medusae and Insects,
maintained that these cells are not derived from the body, but only from
pre-existing germ-cells stored within it--that, in fact, although an egg
gives rise to a hen, a hen does not give rise to an egg, but only keeps
inside her a store of embryonic eggs which mature and are laid as the
time comes round. The theory had to be modified to suit the facts of
regeneration and vegetative reproduction, but in essence it was accepted
by the biological world and is the orthodox opinion (if such a word may
be used in Science) at the present day. The difference between the two
views is not only of theoretical interest, for it involves the whole
question of whether characteristics acquired by an individual during its
life in response to external conditions can or cannot be transmitted to
offspring. If the germ-cells contain representatives of all parts of the
body, modifications impressed on the body during its life may at least
possibly be transmitted to offspring born after the modifications have
taken place. If, however, the germ-cells are independent of the rest of
the body, and only stored within it for safe-keeping like a deed-box in
the vaults of a bank, it would seem impossible for any environmental
influence, whether for good or ill, to take effect on the offspring.
This controversy on the heritability of 'acquired characters' was one of
the most important towards the end of last century, and although the
majority of biologists now follow Weis