ind, all gave rise to like
offspring, and thus arose the idea of distinct 'species' of plants and
animals.

It must be remembered, however, that for a long time 'the world' was
believed to be limited to a few districts surrounding the Eastern
Mediterranean, and the kinds or 'species' of animals and plants were
supposed to number a few scores or at most hundreds. This being the
case, the sudden stocking of 'the world' with its complement of animals
and plants would be thought a comparatively simple operation, and the
violent destruction of the whole a scarcely serious result. Even the
possibility of the preservation of pairs of all the different species,
in a ship of moderate dimensions, was one that was easily entertained
and was not calculated to awaken either surprise or incredulity.

But how different is the problem as it now presents itself to us! In the
year 1900 Professor S. H. Vines of Oxford estimated that the number of
'species' of plants that have been described could be little short of
200,000, and that future studies, especially of the lower microscopic
forms, would probably bring that number up to 300,000[5]. Last year, Mr
A. E. Shipley of Cambridge, basing his estimate on the earlier one of Dr
Guenther, came to the conclusion that the number of described animals
must also exceed 300,000[6]. On the lowest estimate then we must place
the number of known species of plants and animals, living on the globe,
as 600,000! And if we consider the numbers of new forms of plants and
animals that every year are being described by naturalists--about 1500
plants and 1200 animals--if we take into account the inaccessible or as
yet unvisited portions of the earth's surface, the very imperfectly
known depths of the sea, and, in addition to these, the almost infinite
varieties of minute and microscopic forms, I think every competent judge
would consider _a million_ as being probably an estimate below, rather
than above, the number of 'species' now existing on the earth!

While some of these species are very widely distributed over the earth's
surface, or in the waters of the oceans, seas, lakes and rivers, there
are others which are as strikingly limited in their range. Many of the
myriad forms of insect-life pass their whole existence, and are
dependent for food, on a particular species of plant. Not a few animals
and plants are parasitical, and can only live in the interior or on the
outside of other plants and animals.