t the foregoing is still felt to be true by those who accept
evolution, may be seen from the following passage, taken from Mr.
Darwin's 'Origin of Species':--

"As all the organic beings which have ever lived can be arranged within
a few great classes; and as all within each class have, according to our
theory, been connected together by fine gradations, the best, and if our
collections were nearly perfect, the only possible arrangement would be
genealogical: descent being the hidden bond of connection which
naturalists have been seeking under the term of the Natural System. On
this view, we can understand how it is that in the eyes of most
naturalists, the structure of the embryo is even more important for
classifications than that of the adult."[217]

In his second chapter Lamarck deals with the importance of comparative
anatomy, and the study of homologous structures. These indicate a sort
of blood relationship between the individuals in which they are found,
and are our safest guide to any natural system of classification. Their
importance is not confined to the study of classes, families, or even
species; they must be studied also in the individuals of each species,
as it is thus only, that we can recognize either identity or difference
of species. The results arrived at, however, are only trustworthy over a
limited period, for though the individuals of any species commonly so
resemble one another at any given time, as to enable us to generalize
from them, at the date of our observing them, yet species are not fixed
and immutable through all time: they change, though with such extreme
slowness that we do not observe their doing so, and when we come upon a
species that _has_ changed, we consider it as a new one, and as having
always been such as we now see it.[218]

"It is none the less true that when we compare the same kind of organs
in different individuals, we can quickly and easily tell whether they
are very like each other or not, and hence, whether the animals or
plants in which they are found, should be set down as members of the
same or of a different species. It is only therefore the general
inference drawn from the apparent immutability of species, that has
been too inconsiderately drawn.[219]

"The analogies and points of agreement between living organisms, are
always incomplete when based upon the consideration of any single organ
only. But though still incomplete, they will be much more important
a