THE task which evolution has set itself may be described in the words of Professor E. Ray Lankester: “It is the aim or business of those occupied with biology to assign living things, in all their variety of form and activity, to the one set of forces recognised by the physicist and chemist. Just as the astronomer accounts for the heavenly bodies and their movements by the laws of motion and the property of attraction, as the geologist explains the present state of the earth's crust by the long-continued action of the same forces which at this moment are studied and treated in the form of ‘laws’ by physicists and chemists; so the biologist seeks to explain in all its details the long process of the evolution of the innumerable forms of life now existing, or which have existed in the past, as a necessary outcome, an automatic product, of these same forces.” (Encyc. Brit., vol. xxiv., p. 799a.) Again: “It was reserved for Charles Darwin, in the year 1859, to place the whole theory of organic evolution on a new footing, and by his discovery of a mechanical cause actually existing and demonstrable by which organic evolution must be brought about to entirely change the attitude in regard to it of even the most rigid exponents of the scientific method” (p. 801b).