The Descent of Man

those forms which at present appear to be specifically
distinct, were found to graduate into
each other by close steps, they would usually
be ranked as mere varieties or races; and this
course has been followed by most naturalists
with respect to the races of man. Nevertheless,
it must be confessed that there are forms, at
least in the vegetable kingdom (19. Prof. Nageli
has carefully described several striking cases in
his 'Botanische Mittheilungen,' B. ii. 1866, ss.
294-369. Prof. Asa Gray has made analogous
remarks on some intermediate forms in the
Compositae of N. America.), which we cannot
avoid naming as species, but which are connected
together by numberless gradations, independently
of intercrossing.
Some naturalists have lately employed the term
"sub-species" to designate forms which possess
many of the characteristics of true species, but
which hardly deserve so high a rank. Now if
we reflect on the weighty arguments above