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Corresponding changes take place in the arteries, and we shall find that this change in structure is of very great importance in the evolution of the higher types of land-life. The heart of the higher land-animals, we may add, passes through these stages in its embryonic development. Externally the chief change in the Amphibian is the appearance of definite legs.
A very small proportion of them will survive that trial, and they trill be the better organised to maintain themselves and rear their young in the new earth. The remaining land-life of the Coal-forest is confined to worm-like organisms whose remains are not preserved, and land-snails which do not call for further discussion. We may, in conclusion, glance at the progress of life in the waters.
Successive swarms of vegetarians Worms, Molluscs, etc. followed the plant on to the land; and swarms of carnivores followed the vegetarians, and assumed strange, new forms in adaptation to land-life. The migration had probably proceeded throughout the Devonian period, especially from the calmer shores of the inland seas.
The land gives work which is varied, alive, and interesting beyond all town industries, save those, perhaps, of art and the highly-skilled crafts and professions. If we can once get land-life back on to a wide and solid basis, it should hold its own.
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