But many of the earlier forms of life were so enormous and so destructive, that man could by no possibility have debated with them the empire of the globe. The battle would have gone the wrong way for man. It is well that various changes removed these creatures before man appeared. Another consideration is here of great interest; the forms of life which survived their respective cycles, and came down nearly unchanged to our day, were not the strongest and largest creatures, apparently best able to fight their battle and live; but many of the feebler and smaller creatures, which, if we had been spectators of those ancient times, we should have expected to see perish under the encroachments of monsters and dragons of their day. As, for instance, the large, strong, numerous, armor-plated trilobites[22] of the second earth-age perished ages ago, while the little lamp shells live on until now. Far back in the reptile time, little mammal quadrupeds, scarcely larger than rats, ran in the woods, and these types have been continued with various adaptations in the marsupial or pouched animals, like the opossum of our own day, while the vast scale-dressed giants have only left a few of their scattered bones to tell their story. The dragon-fly survives, very like his ancestors of the Triassic period, while the mighty pterodactyles,[23] a kind of reptile bat that pursued the dragon-flies as part of its prey, have gone never to return. The flying reptile has left us only his enormous lithograph upon the ancient rocks, while still each year the jewel-like dragon-fly, once the big beast’s defenceless prey, bursts his brown case, and comes forth informed with light and life.[24] As the poet tells his story:-- “To-day I saw the dragon-fly Come from the wells where he did lie,-- An inner impulse rent the veil, Of his old husk; from head to tail Came out clear plates of sapphire mail. He dried his wings, like gauze they grew; Thro’ copse and pastures wet with dew, A living flash of light he flew.” We should not forget that each one of the earth-building ages had some particular form of animal life which seemed in that age to be king, and conquer the other animals. Also in its own age each of these forms reached its greatest strength and perfection. Then in after ages, when some new type was dominant, the former types that still survived became smaller and more feeble. We have crabs and other crustacea now-a-days, but none so enormous as in the second world-building age when they first appeared. The mollusks,[25] which you call shell-fish,[26] were largest and most numerous in the upper Silurian time. The sea-weeds that flourished with these crabs and mollusks were larger and more splendid than any sea-weeds now, for this is the age of man, and grass, and corn, not of crabs and sea-weeds.