iles. If they really possess any such sense, that
distance would be no bar to their return. I have myself experimented
with Ants, taking them about fifty yards from the nest, and I always
found that they wandered aimlessly about, having evidently not the
slightest idea of their way home. They certainly did not appear to
possess any "sense of direction."

NUMBER OF SPECIES

The total number of species may probably be safely estimated as at least
2,000,000, of which but a fraction have yet been described or named. Of
extinct species the number was probably at least as great. In the
geological history of the earth there have been at least twelve periods,
in each of which by far the greatest number were distinct. The Ancient
Poets described certain gifted mortals as having been privileged to
descend into the interior of the earth, and exercised their imagination
in recounting the wonders thus revealed. As in other cases, however, the
realities of Science have proved far more varied and surprising than the
dreams of fiction. Of these extinct species our knowledge is even more
incomplete than that of the existing species. But even of our
contemporaries it is not too much to say that, as in the case of
plants, there is not one the structure, habits, and life-history of
which are yet fully known to us. The male of the Cynips, which produces
the common King Charles Oak Apple, has only recently been discovered,
those of the root-feeding Aphides, which live in hundreds in every nest
of the yellow Meadow Ant (Lasius flavus) are still unknown; the habits
and mode of reproduction of the common Eel have only just been
discovered; and we may even say generally that many of the most
interesting recent discoveries have relation to the commonest and most
familiar animals.

IMPORTANCE OF THE SMALLER ANIMALS

Whatever pre-eminence Man may claim for himself, other animals have done
far more to affect the face of nature. The principal agents have not
been the larger or more intelligent, but rather the smaller, and
individually less important, species. Beavers may have dammed up many of
the rivers of British Columbia, and turned them into a succession of
pools or marshes, but this is a slight matter compared with the action
of earthworms and insects[17] in the creation of vegetable soil; of the
accumulation of animalcules in filling up harbours and lakes; or of
Zoophytes in the construction of coral islands.

Microscopic animals make