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! Among 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 the 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, geographical races! Mr. Wallace, in
several valuable papers on the various animals, especially on the
Lepidoptera, inhabiting the islands of the great Malayan Archipelago,
shows that they may be classed under four heads, namely, as variable
forms, as local forms, as geographical races or sub-species, and as true
representative species. The first or variable forms vary much within the
limits of the same island. The local forms are moderately constant and
distinct in each separate island; but when all from the several islands
are compared together, the differences are seen to be so slight and
graduated that it is impossible to define or describe them, though
at the same time the extreme forms are sufficiently distinct. The
geographical races or sub-species are local forms completely fixed and
isolated; but as they do not differ from each other by strongly marked
and important characters, "There is no possible test but individual
opinion to determine which of them shall be considered as species and
which as varieties." Lastly, representative species fill the same
place in the natural economy of each island as do the local forms and
sub-species; but as they are distinguished from each other by a greater
amount of difference than that between the local forms and sub-species,
they are almost universally ranked by naturalists as true species.
Nevertheless, no certain criterion can possibly be given by which
variable forms, local forms, sub species