But it is during periods of change that life undergoes its most rapid modifications, and under hardship that it learns its hardest lessons. As conditions revert towards warmth and moisture again we find a new series of animal and plant forms established, We find in the record the remains of vertebrated animals that laid eggs which, instead of hatching out tadpoles which needed to live for a time in water, carried on their development before hatching to a stage so nearly like the adult form that the young could live in air from the first moment of independent existence. Gills had been cut out altogether, and the gill slits only appeared as an embryonic phase. These new creatures without a tadpole stage were the Reptiles. Concurrently there had been a development of seed-bearing trees, which could spread their seed, independently of swamp or lakes. There were now palmlike cycads and many tropical conifers, though as yet there were no flowering plants and no grasses. There was a great number of ferns. And there was now also an increased variety of insects. There were beetles, though bees and butterflies had yet to come. But all the fundamental forms of a new real land fauna and flora had been laid down during these vast ages of severity. This new land life needed only the opportunity of favourable conditions to flourish and prevail. A FOSSIL ICHTHYOSAURUS, A MESOZOIC FISH-LIZARD A FOSSIL ICHTHYOSAURUS, A MESOZOIC FISH-LIZARD Found in the Lower Lias in Somersetshire _Nat. Hist. Mus._ Age by age and with abundant fluctuations that mitigation came. The still incalculable movements of the earth’s crust, the changes in its orbit, the increase and diminution of the mutual inclination of orbit and pole, worked together to produce a great spell of widely diffused warm conditions. The period lasted altogether, it is now supposed, upwards of two hundred million years. It is called the Mesozoic period, to distinguish it from the altogether vaster Palæozoic and Azoic periods (together fourteen hundred millions) that preceded it, and from the Cainozoic or new life period that intervened between its close and the present time, and it is also called the Age of Reptiles because of the astonishing predominance and variety of this form of life. It came to an end some eighty million years ago.