It is impossible, we must admit, to fix dates, except in a few cases,
relatively recent; but there is a smack of modernity in some striking
devices which we can observe in operation to-day. Thus no one will
dispute the statement that spiders are thoroughly terrestrial animals
breathing dry air, but we have the fact of the water-spider conquering
the under-water world. There are a few spiders about the seashore, and a
few that can survive douching with freshwater, but the particular case
of the true water-spider, _Argyroneta natans_, stands by itself because
the creature, as regards the female at least, has _conquered_ the
sub-aquatic environment. A flattish web is woven, somehow, underneath
the water, and pegged down by threads of silk. Along a special vertical
line the mother spider ascends to the surface and descends again, having
entangled air in the hairs of her body. She brushes off this air
underneath her web, which is thereby buoyed up into a sort of dome. She
does this over and over again, never getting wet all the time, until the
domed web has become like a diving-bell, full of dry air. In this
eloquent anticipation of man's rational device, this creature--far from
being endowed with reason--lays her eggs and looks after her young. The
general significance of the facts is that when competition is keen, a
new area of exploitation is a promised land. Thus spiders have spread
over all the earth except the polar areas. But here is a spider with
some spirit of adventure, which has endeavoured, instead of trekking, to
find a new corner near at home. It has tackled a problem surely
difficult for a terrestrial animal, the problem of living in great part
under water, and it has solved it in a manner at once effective and
beautiful.