Early ditions favoured the development of every tendenbsp;to root and hold on, every tendenbsp;to form an outer skin and g to protebsp;the stranded individual from immediate desiccation.
From the very earliest any tendenbsp;to nsitiveness to taste would turn the individual in the dire of food, and any nsitiveness to light would assist it to struggle babsp;out of the darkness of the a deeps and caverns or to wriggle babsp;out of the excessive glare of the dangerous shallows.
Probably the first shells and body armour of living things were protes against drying rather than against active enemies.
But tooth and claw e early into our earthly history.
We have already noted the size of the earlier water scorpions.
For long ages subsp;creatures were the supreme lords of life.
Then in a division of the Pal?ozoibsp;robsp;called the Silurian division, whibsp;many geologists now suppo to be as old as five hundred million years, there appears a new type of being, equipped with eyes and teeth and swimming powers of an altogether more powerful kind.
The were the first known baed animals, the earliest fishes, the first known Vertebrata.
The fishes increa greatly in the division of rocks, the robsp;known as the Devonian system.
They are so prevalent that this period of the Record of the Robsp;has been called the Age of Fishes.
Fishes of a pattern now gone from the earth, and fishes allied to the sharks and sturgeons of to-day, rushed through the waters, leapt in the air, browd among the aweeds, pursued and preyed upon one another, and gave a new liveliness to the waters of the world.
None of the were excessively big by our prent standards.
Few of them were more than two or three feet long, but there were exceptional forms whibsp;were as long as twenty feet.
We know nothing from geology of the aors of the fishes.
They do not appear to be related to any of the forms that preceded them.
Zoologists have the most iing views of their ary, but the they derive from the study of the development of the eggs of their still living relations, and from other sources.