The Origin of Species | Page 5

animal or plant, which is
distinctly definable from all others, by certain constant, and not merely
sexual, morphological peculiarities. Thus horses form a species,
because the group of animals to which that name is applied is
distinguished from all others in the world by the following constantly
associated characters. They have--1, A vertebral column; 2, Mammae;
3, A placental embryo; 4, Four legs; 5, A single well-developed toe in
each foot provided with a hoof; 6, A bushy tail; and 7, Callosities on
the inner sides of both the fore and the hind legs. The asses, again, form
a distinct species, because, with the same characters, as far as the fifth
in the above list, all asses have tufted tails, and have callosities only on
the inner side of the fore-legs. If animals were discovered having the
general characters of the horse, but sometimes with callosities only on
the fore-legs, and more or less tufted tails; or animals having the
general characters of the ass, but with more or less bushy tails, and
sometimes with callosities on both pairs of legs, besides being
intermediate in other respects--the two species would have to be
merged into one. They could no longer be regarded as morphologically
distinct species, for they would not be distinctly definable one from the
other.
However bare and simple this definition of species may appear to be,
we confidently appeal to all practical naturalists, whether zoologists,
botanists, or palaeontologists, to say if, in the vast majority of cases,
they know, or mean to affirm anything more of the group of animals or
plants they so denominate than what has just been stated. Even the
most decided advocates of the received doctrines respecting species
admit this.
"I apprehend," says Professor Owen*, "that few naturalists nowadays,
in describing and proposing a name for what they call 'a new species,'
use that term to signify what was meant by it twenty or thirty years ago;

that is, an originally distinct creation, maintaining its primitive
distinction by obstructive generative peculiarities. The proposer of the
new species now intends to state no more than he actually knows; as,
for example, that the differences on which he founds the specific
character are constant in individuals of both sexes, so far as observation
has reached; and that they are not due to domestication or to artificially
superinduced external circumstances, or to any outward influence
within his cognizance; that the species is wild, or is such as it appears
by Nature."
[footnote] *On the Osteology of the Chimpanzees and Orangs:
Transactions of the Zoological Society, 1858.
If we consider, in fact, that by far the largest proportion of recorded
existing species are known only by the study of their skins, or bones, or
other lifeless exuvia; that we are acquainted with none, or next to none,
of their physiological peculiarities, beyond those which can be deduced
from their structure, or are open to cursory observation; and that we
cannot hope to learn more of any of those extinct forms of life which
now constitute no inconsiderable proportion of the known Flora and
Fauna of the world: it is obvious that the definitions of these species
can be only of a purely structural, or morphological, character. It is
probable that naturalists would have avoided much confusion of ideas
if they had more frequently borne the necessary limitations of our
knowledge in mind. But while it may safely be admitted that we are
acquainted with only the morphological characters of the vast majority
of species--the functional or physiological, peculiarities of a few have
been carefully investigated, and the result of that study forms a large
and most interesting portion of the physiology of reproduction.
The student of Nature wonders the more and is astonished the less, the
more conversant he becomes with her operations; but of all the
perennial miracles she offers to his inspection, perhaps the most worthy
of admiration is the development of a plant or of an animal from its
embryo. Examine the recently laid egg of some common animal, such
as a salamander or newt. It is a minute spheroid in which the best
microscope will reveal nothing but a structureless sac, enclosing a

glairy fluid, holding granules in suspension. But strange possibilities lie
dormant in that semi-fluid globule. Let a moderate supply of warmth
reach its watery cradle, and the plastic matter undergoes changes so
rapid, yet so steady and purposelike in their succession, that one can
only compare them to those operated by a skilled modeller upon a
formless lump of clay. As with an invisible trowel, the mass is divided
and subdivided into smaller and smaller portions, until it is reduced to
an aggregation of granules not too large to build withal the finest
fabrics of the nascent organism. And, then, it is