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 which kingdom they should be referred. As
Professor Asa Gray has remarked, "the spores and other reproductive bodies
of many of the lower algae may claim to have first a characteristically
animal, and then an unequivocally vegetable existence." Therefore, on the
principle of natural selection with divergence of character, it does not
seem incredible that, from some such low and intermediate form, both
animals and plants may have been developed; and, if we admit this, we must
likewise admit that all the organic beings which have ever lived on this
earth may be descended from some one primordial form.
Pages:
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779