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."

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 exuviae; 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