IN the present volume I have attempted to summarise and complete my half-century of thought and work on the Darwinian theory of evolution. In several directions I have extended the scope and application of the theory, and have shown that it is capable Of explaining many of the phenomena Of living things hitherto thought to be beyond its range. Among these are the detailed distribution of plants and animals, which I have discussed at some length. It occupies about one-fourth Of the volume (chapters II. To and brings out certain facts and conclusions which I believe will be Of interest to all plant-lovers, and also be not without a certain value to botanists. Next in importance are three chapters (x., XI and XII.) devoted to a general review of the Geological Record and a discussion of the various problems arising out Of it. Some of the conclusions to which this examination leads us are, I believe, both important and Of much general interest.