define, or even conjecture, which are the created forms of life, and which
are those produced by secondary laws. They admit variation as a _vera
causa_ in one case, they arbitrarily reject it in another, without
assigning any distinction in the two cases. The day will come when this
will be given as a curious illustration of the blindness of preconceived
opinion. These authors seem no more startled at a miraculous act of
creation than at an ordinary birth. But do they really believe that at
innumerable periods in the earth's history certain elemental atoms have
been commanded suddenly to flash into living tissues? Do they believe that
at each supposed act of creation one individual or many were produced? Were
all the infinitely numerous kinds of animals and plants created as eggs or
seed, or as full grown? and in the case of mammals, were they created
bearing the false marks of nourishment from the mother's womb? Although
naturalists very properly demand a full explanation of every difficulty
from those who believe in the mutability of species, on their own side they
ignore the whole subject of the first appearance of species in what they
consider reverent silence.

It may be asked how far I extend the doctrine of the modification of
species. The question is difficult to answer, because the more distinct the
forms are which we may consider, by so much the arguments fall away in
force. But some arguments of the greatest weight {484} extend very far. All
the members of whole classes can be connected together by chains of
affinities, and all can be classified on the same principle, in groups
subordinate to groups. Fossil remains sometimes tend to fill up very wide
intervals between existing orders. Organs in a rudimentary condition
plainly show that an early progenitor had the organ in a fully developed
state; and this in some instances necessarily implies an enormous amount of
modification in the descendants. Throughout whole classes various
structures are formed on the same pattern, and at an embryonic age the
species closely resemble each other. Therefore I cannot doubt that the
theory of descent with modification embraces all the members of the same
class. I believe that animals have descended from at most only four or five
progenitors, and plants from an equal or lesser number.

Analogy would lead me one step further, namely, to the belief that all
animals and plants have descended from some one prototype. But analogy