lows a path of its own. As well as internal tides which swing
to and fro about an average level, there is a drift which carries the
fauna bodily along an 'irretraceable course.'" This is partly due to
considerable changes of climate, for climate calls the tune to which
living creatures dance, but it is also due to new departures among the
animals themselves. We need not go back to the extinct animals and lost
faunas of past ages--for Britain has plenty of relics of these--which
"illustrate the reality of the faunal drift," but it may be very useful,
in illustration of evolution in being, to notice what has happened in
Scotland since the end of the Great Ice Age.

Some nine thousand years ago or more, certain long-headed,
square-jawed, short-limbed, but agile hunters and fishermen, whom we
call Neolithic Man, established themselves in Scotland. What was the
state of the country then?

It was a country of swamps, low forests of birch, alder, and willow,
fertile meadows, and snow-capped mountains. Its estuaries penetrated
further inland than they now do, and the sea stood at the level of
the Fifty-Foot Beach. On its plains and in its forests roamed many
creatures which are strange to the fauna of to-day--the Elk and the
Reindeer, Wild Cattle, the Wild Boar and perhaps Wild Horses, a
fauna of large animals which paid toll to the European Lynx, the
Brown Bear and the Wolf. In all likelihood, the marshes resounded to
the boom of the Bittern and the plains to the breeding calls of the
Crane and the Great Bustard.

Such is Dr. Ritchie's initial picture.

[Illustration: LIFE-HISTORY OF A FROG

1, Before hatching; 2, newly hatched larvae hanging on to water-weed; 3,
with external gills; 4, external gills are covered over and are
absorbed; 5, limbless larva about a month old with internal gills; 6,
tadpole with hind-legs, about two months old; 7, with the fore-limbs
emerging; 8, with all four legs free; 9, a young frog, about three
months old, showing the almost complete absorption of the tail and the
change of the tadpole mouth into a frog mouth.]

[Illustration: _Photo: J. J. Ward. F.E.S._

HIND-LEG OF WHIRLIGIG BEETLE WHICH HAS BECOME BEAUTIFULLY MODIFIED FOR
AQUATIC LOCOMOTION

The flattened tips form an expanding "fan" or paddle, which opens and
closes with astonishing rapidity. The closing of the "fan," like the
"feathering" of an oar, reduces friction when the leg is being mo