w quadruped might have been observed to
appear suddenly in those parts, of England or France which had been most
thoroughly investigated;--that naturalists might have been able to show
that no such living being inhabited any other region of the globe, and
that there was no tradition of anything similar having before been
observed in the district where it had made its appearance.

Now, although this objection may seem plausible, yet its force will be
found to depend entirely on the rate of fluctuation which we suppose to
prevail in the animate world, and on the proportion which such
conspicuous subjects of the animal and vegetable kingdoms bear to those
which are less known and escape our observation. There are, perhaps,
more than a million species of plants and animals, exclusive of the
microscopic and infusory animalcules, now inhabiting the terraqueous
globe. The terrestrial plants may amount, says De Candolle, to somewhere
between 110,000 and 120,000;[992] but the data on which this conjecture
is founded are considered by many botanists to be vague and
unsatisfactory. Sprengel only enumerated, in 1827, about 31,000 known
phaenogamous, and 6000 cryptogamous plants; but that naturalist omitted
many, perhaps 7000 phaenogamous, and 1000 cryptogamous species. Mr.
Lindley, in a letter to the author in 1836, expressed his opinion that
it would be rash to speculate on the existence of more than 80,000
phaenogamous, and 10,000 cryptogamous plants. "If we take," he says, in a
letter to the author on this subject, "37,000 as the number of published
phaenogamous species, and then add, for the undiscovered species in Asia
and New Holland, 15,000, in Africa 10,000, and in America 18,000, we
have 80,000 species; and if 7000 be the number of published cryptogamous
plants, and we allow 3000 for the undiscovered species (making 10,000),
there would then be, on the whole, 90,000 species." But since that
period one catalogue, as I learn from Dr. J. Hooker, contains a list of
the names of 78,000 phaenogamous plants which had been published before
1841.

It was supposed by Linnaeus that there were four or five species of
insects in the world for each phaenogamous plant: but if we may judge
from the relative proportion of the two classes in Great Britain, the
number of insects must be still greater; for the total number of British
insects, "according to the last census," is about 12,500;[993] whereas
there are only 1500 phaenogamous plant