e
same thing; she believed that he must be immortal. I am sure that he
never was born."

[Sidenote: Two modes of action.] Two modes have been presented by which
we may conceive of the influence of physical agents upon organic forms.
Their long persistent action upon the individual may give rise to
modifications, developing one part, stunting another; and such
variations, being transmitted in an hereditary way, may become firmly
fixed at last. Thus a given plant may, in the course of ages, under the
influence of unremittingly acting physical conditions, undergo a
permanent change, and a really new plant arise as soon as, through the
repetitions of successive generations, the modifications have become so
thorough, so profound, as to be capable of transmission with certainty.
Perhaps this is what has taken place with many of our kitchen-garden
plants, of which the special varieties may be propagated by seeds. But
there is another mode by which that result may be reached, even if we
decline the doctrine of St. Augustine, who, in his work "De Civitate
Dei," shows how islands may be peopled with animals by "spontaneous
generation." All organic forms originally spring from a simple cell, the
development of which, as indicated by the final form attained, is
manifestly dependent on the physical conditions it has been exposed to
during its course. If those conditions change, that final form must
change correspondingly; and in this manner, since all organic beings
come from the same starting-point--the same cell, as has been said,
which helplessly submits to whatever impression may be put upon it--the
issue is the same as though a transformation or transmutation had
occurred, since the descendant is not like its ancestors. Such a manner
of considering these changes is in harmony with our best physiological
knowledge, since it does not limit itself to a small portion of the life
of an individual, but embraces its whole cycle or career. For the more
complete examination of this view I may refer to the second chapter of
the second book of my "Physiology."

[Sidenote: Problem of the modification of forms.] But here has arisen
the inquiry, Does the modification of organic forms depend exclusively
on the impressions of external influences, or is it due to a nisus or
force of development residing in the forms themselves?

Whether we consider the entire organic series in its succession, or the
progress of an individual in his developme