also from the speculations of
mediaeval writers, the molecules of Bonnet and of Buffon almost anticipated
the hypothesis of Pangenesis. According to the last-named author,[228]
organic particles from every part of the body assemble in the sexual
secretions, and by their union build up the embryo, each particle taking
its due place, and occupying in the offspring a similar position to that
which it occupied in the parents. In 1849 Professor Owen, in his treatise
on "Parthenogenesis," put forward another conception. According to this,
the cells resulting from the subdivision of the germ-cell preserve their
developmental force, unless employed in building up definite organic
structures. In certain creatures, and in certain parts of other creatures,
germ-cells unused are stored up, and by their agency lost limbs and {218}
other mutilations are repaired. Such unused products of the germ-cell are
also supposed to become located in the generative products.

According to Mr. Herbert Spencer, in his "Principles of Biology," each
living organism consists of certain so-called "physiological units." Each
of these units has an innate power and capacity, by which it tends to build
up and reproduce the entire organism of which it forms a part, unless in
the meantime its force is exhausted by its taking part in the production of
some distinct and definite tissue--a condition somewhat similar to that
conceived by Professor Owen.

Now, at first sight, Mr. Darwin's atomic theory appears to be more simple
than any of the others. It has been objected that while Mr. Spencer's
theory requires the assumption of an innate power and tendency in each
physiological unit, Mr. Darwin's, on the other hand, requires nothing of
the kind, but explains the evolution of each individual by purely
mechanical conceptions. In fact, however, it is not so. Each gemmule,
according to Mr. Darwin, is really the seat of powers, elective affinities,
and special tendencies as marked and mysterious as those possessed by the
physiological unit of Mr. Spencer, with the single exception that the
former has no tendency to build up the whole living, complex organism of
which it forms a part. Some may think this an important distinction, but it
can hardly be so, for Mr. Darwin considers that his gemmule has the innate
power and tendency to build up and transform itself into the whole living,
complex cell of which it forms a part; and the one tendency is, in
principle, fu