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 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.
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