cing
back also their individual developments to the first differentiation of the
simplest cell, they followed out the unity of the plan of the organic
kingdoms--which hitherto had been maintained only ideally and proclaimed as
a philosophic postulate--farther and deeper into the sphere of empiric
reality. We must mention, moreover, the great palaeontological discoveries
which, from the first foraminifera of the Cambrian formations up to the
historical period of man, showed a great progressive scale in the
appearance of the organisms and a very wide relationship between this scale
and the natural systems of botany and zooelogy; and, finally, the principles
of geology, which, under the leadership of Sir Charles Lyell, starting from
the idea of an identity of the powers which were active in former times
with those of the present, attempted to explain the most violent of the
changes in the earth's crust in former times by causes active to-day. This
often explains prodigious effects--such as the elevation and settling of
entire mountains {37} and continents--by the constant and related action of
the slightest causes and most gradual steps; it opens the perspective into
vast epochs of long and numerous geological periods; and sometimes, where
scientists like Cuvier and Agassiz have supposed the most complete
cataclysms and the most universal revolutions of the globe, there prove to
have been only gradual changes with revolutions very partially and locally
limited.

Finally, if we take into consideration the grand discoveries which
strikingly illustrate the connection in extent and quality between the
universe and all its agencies and powers--such as Robert von Mayer's
discovery of the conservation of force and of the mechanical equivalent of
heat, or the spectrum analysis and the information which it gives us by
ever-increasing evidences of the identity of the cosmic and telluric
substances--we may venture to say that the scientific and intellectual
ground was well prepared for a theory which takes the origin of organisms
into this common relationship of the essential unity and development of the
universe.

Only one thing more remained to complete the hypothesis offered by Lamarck,
of the _fact_ of a development of species by a new and more satisfactory
answer to the question as to the _manner_ of their development. The task of
answering in a more comprehensive and scientific way the question as to the
manner of development