s doubtful nature are far from uncommon cannot be
disputed. Compare the several floras of Great Britain, of France or of the
United States, drawn up by different botanists, and see what a surprising
number of forms have been ranked by one botanist as good species, and by
another as mere varieties. Mr. H. C. Watson, to whom I lie under deep
obligation for assistance of all kinds, has marked for me 182 British
plants, which are generally considered as varieties, but which have all
been ranked by botanists as species; and in making this list he has omitted
many trifling varieties, but which nevertheless have been ranked by some
botanists as species, and he has entirely omitted several highly
polymorphic genera. Under genera, including the most polymorphic forms, Mr.
Babington gives 251 species, whereas Mr. Bentham gives only 112,--a
difference of 139 doubtful forms! Amongst animals which unite for each
birth, and which are highly locomotive, doubtful forms, ranked by one
zoologist as a species and by another as a variety, can rarely be found
within the same country, but are common in separated areas. How many of
those birds and insects in North America and Europe, which differ very
slightly from each other, have been ranked by one eminent naturalist as
undoubted species, and by another as varieties, or, as they are often
called, as geographical races! Many years ago, when comparing, and seeing
others compare, the birds from the separate islands of the Galapagos
Archipelago, both one with another, and with those from the American
mainland, I was much struck how entirely vague and arbitrary is the
distinction between species and varieties. On the islets of the little
Madeira group there are many insects which are characterized as varieties
in Mr. Wollaston's admirable work, but which it cannot {49} be doubted
would be ranked as distinct species by many entomologists. Even Ireland has
a few animals, now generally regarded as varieties, but which have been
ranked as species by some zoologists. Several most experienced
ornithologists consider our British red grouse as only a strongly-marked
race of a Norwegian species, whereas the greater number rank it as an
undoubted species peculiar to Great Britain. A wide distance between the
homes of two doubtful forms leads many naturalists to rank both as distinct
species; but what distance, it has been well asked, will suffice? if that
between America and Europe is ample, will that betwee