Experiments in Locomotion

It is very interesting to think of the numerous types of locomotion which animals have discovered—pulling and punting, sculling and rowing, and of the changes that are rung on these four main methods. How striking is the case of the frilled lizard (Chlamydosaurus) of Australia, which at the present time is, as it were, experimenting in bipedal progression—always a rather eventful thing to do. It gets up on its hind-legs and runs totteringly for a few feet, just like a baby learning to walk.

How beautiful is the adventure which has led our dipper or water-ouzel—a bird allied to the wrens—to try walking and flying under water! How admirable is the volplaning of numerous parachutists—"flying fish," "flying frog," "flying dragon," "flying phalanger," "flying squirrel," and more besides, which take great leaps through the air. For are these not the splendid failures that might have succeeded in starting new modes of flight?

Most daring of all, perhaps, are the aerial journeys undertaken by many small spiders. On a breezy morning, especially in the autumn, they mount on gate-posts and palings and herbage, and, standing with their head to the wind, pay out three or four long threads of silk. When the wind tugs at these threads, the spinners let go, and are borne, usually back downwards, on the wings of the wind from one parish to another. It is said that if the wind falls they can unfurl more sail, or furl if it rises. In any case, these wingless creatures make aerial journeys. When tens of thousands of the used threads sink to earth, there is a "shower of gossamer." On his Beagle voyage Darwin observed that vast numbers of small gossamer spiders were borne on to the ship when it was sixty miles distant from the land.

THE AUSTRALIAN FRILLED LIZARD, WHICH IS AT PRESENT TRYING TO BECOME A BIPED

When it gets up on its hind-legs and runs for a short distance it folds its big collar round its neck.

A CARPET OF GOSSAMER

The silken threads used by thousands of gossamer spiders in their migrations are here seen entangled in the grass, forming what is called a shower of gossamer. At the edge of the grass the gossamer forms a curtain, floating out and looking extraordinarily like waves breaking on a seashore.

THE WATER-SPIDER

The spider is seen just leaving its diving-bell to ascend to the surface to capture air.

The spider jerks its body and legs out at the surface and then dives—

—carrying with it what looks like a silvery air-bubble—air entangled in the hair.

The spider reaches its air-dome. Note how the touch of its legs indents the inflated balloon.

Running down the side of the nest, the spider

—brushes off the air at the entrance, and the bubble ascends into the silken balloon.

Photos: J. J. Ward, F.E.S.

New Devices

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.

In Conclusion

We have given but a few representative illustrations of a great theme. When we consider the changefulness of living creatures, the transformations of cultivated plants and domesticated animals, the gradual alterations in the fauna of a country, the search after new haunts, the forming of new habits, and the discovery of many inventions, are we not convinced that Evolution is going on? And why should it stop?