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CAUSATION AND EVOLUTION.
Whence
is
ence ?
its primary stage, says the Biologist, every germ consists of a substance that is uniform throughout, both in texture and chemical the differcomposition. The first step, in the development of the germ, is the appearance of a difference between the two parts in this substance or as the phenomenon is called in physiological language-'differentiation'. And the question is, whence is the difference or this ‘differentiation'? In the primary stage of the germ, it was all uniform both in texture and composition. But there appears a difference in the same afterwards. The substantial cause being the same, What is it that accounts for the difference ? Reason whispers that there must be something working from within, some cause behind it. But what is it? "No thoughtful person," to speak in the language of Wallace, “can Wallace at contemplate without amazement the phenomena presented by the development of animals. We see the most diverse forms-a mollusc, a frog, and a mammal-arising from apparently identical primitive cells and progressing for a time by very similar initial changes but thereafter each persuing its
hault.
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