ially when man interferes,
is not necessarily progressive. That depends on the nature of the sieves
with which the living materials are sifted. As Dr. Ritchie well says,
the standard of the wild fauna as regards size has fallen and is
falling, and it is not in size only that there is loss, there is a
deterioration of quality. "For how can the increase of Rabbits and
Sparrows and Earthworms and Caterpillars, and the addition of millions
of Rats and Cochroaches and Crickets and Bugs, ever take the place of
those fine creatures round the memories of which the glamour of
Scotland's past still plays--the Reindeer and the Elk, the Wolf, the
Brown Bear, the Lynx, and the Beaver, the Bustard, the Crane, the
Bumbling Bittern, and many another, lost or disappearing." Thus we see
again that evolution is going on.

Sec. 3

The Adventurers

All through the millions of years during which animals have tenanted the
earth and the waters under the earth, there has been a search for new
kingdoms to conquer, for new corners in which to make a home. And this
still goes on. _It has been and is one of the methods of evolution to
fill every niche of opportunity._ There is a spider that lives inside a
pitcher-plant, catching some of the inquisitive insects which slip down
the treacherous internal surface of the trap. There is another that
makes its home in crevices among the rocks on the shore of the
Mediterranean, or even in empty tubular shells, keeping the water out,
more or less successfully, by spinning threads of silk across the
entrance to its retreat. The beautiful brine-shrimp, _Artemia salina_,
that used to occur in British salterns has found a home in the dense
waters of the Great Salt Lake of Utah. Several kinds of earthworms have
been found up trees, and there is a fish, Arges, that climbs on the
stones of steep mountain torrents of the Andes. The intrepid explorers
of the _Scotia_ voyage found quite a number of Arctic terns spending our
winter within the summer of the Antarctic Circle--which means girdling
the globe from pole to pole; and every now and then there are incursions
of rare birds, like Pallas's Sand-grouse, into Britain, just as if they
were prospecting in search of a promised land. Twice or thrice the
distinctively North American Killdeer Plover has been found in Britain,
having somehow or other got across the Atlantic. We miss part of the
meaning of evolution if we do not catch this note of insurgence and
adven