nt, the orderly course
presented might seem to indicate that the operation is taking place
under a law--an orderly progression being always suggestive of the
operation of law. But a philosophical caution must, however, be here
exercised; for deceptive appearances may lead us into the error of
imputing to such a law, impressed by the Creator on the developing
organism, that which really belongs to external physical conditions,
which, on their part, are following a law of their own. What is here
meant may be illustrated by the facts that occur on the habitable
surface of a planet suffering a gradual decline of heat. [Sidenote:
Three solutions of it.] On such a surface a succession of vegetable
types might make its appearance, and, as these different types emerged
or were eliminated, we might speak of the events as creations and
extinctions, and therefore as the acts of God. Or, in the second place,
we might refer them to an intrinsic force of development imparted to
each germ, which reached in due season its maximum, and then declined
and died out; and, comparing each type with its preceding and succeeding
ones, the interrelation might be suggested to us of the operation of a
controlling law. Or, in the third place, we might look to the external
physical condition--the decline of heat--itself taking place at a
determinate rate under a mathematical law, and drawing in its
consequences the organic variations observed.

Now the first of these explanations in reality means the arbitrary and
unchallengeable will of God, who calls into existence, and extinguishes
according to his sovereign pleasure, whatever he pleases; the orderly
progression we notice becoming an evidence that his volitions are not
erratic, but are according to pure reason. The second implies that there
has been impressed upon every germ a law of continuous organic
variation--it might have been through the arbitrary fiat of God. The
third implies that the successive types owe their appearance and
elimination to a physical influence, which is itself varying under a
strict mathematical necessity; for the law of cooling, which the
circumstances force on our attention, is such a strict mathematical
necessity.

[Sidenote: Their relative probability.] If at this point we balance the
probabilities of these three explanations, we shall perhaps find
ourselves biassed toward the last, as physiologists have been, because
of its rigorous scientific aspect, and should n