tions. Under a scientific point of
view, and as leading to further investigation, but little advantage
is gained by believing that new forms are suddenly developed in an
inexplicable manner from old and widely different forms, over the old
belief in the creation of species from the dust of the earth.

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 consider, by so much the arguments in favour of
community of descent become fewer in number and less in force. But some
arguments of the greatest weight extend very far. All the members of
whole classes are connected together by a chain of affinities, and all
can be classed 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 condition, and this in some
cases implies an enormous amount of modification in the descendants.
Throughout whole classes various structures are formed on the same
pattern, and at a very early age the embryos closely resemble each
other. Therefore I cannot doubt that the theory of descent with
modification embraces all the members of the same great class or
kingdom. I believe that animals are 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 are descended from some one prototype. But analogy
may be a deceitful guide. Nevertheless all living things have much in
common, in their chemical composition, their cellular structure, their
laws of growth, and their liability to injurious influences. We see
this even in so trifling a fact as that the same poison often similarly
affects plants and animals; or that the poison secreted by the gall-fly
produces monstrous growths on the wild rose or oak-tree. With all
organic beings, excepting perhaps some of the very lowest, sexual
reproduction seems to be essentially similar. With all, as far as is at
present known, the germinal vesicle is the same; so that all
organisms start from a common origin. If we look even to the two main
divisions--namely, to the animal and vegetable kingdoms--certain
low forms are so far intermediate in character that naturalists have
disputed to