Page:The advancement of science by experimental research - the Harveian oration, delivered at the Royal College of Physicians, June 27th, 1883 (IA b24869958).pdf/36

32 and on animals? and perhaps none of his works are more attractive than his investi. gations on earth worms; in which he shews, that animals hitherto regarded as of but little interest and service in the economy of nature are of the greatest value and de- signed to be of incalculable benefit to man. Darwin proves that animals undergo changes greater or less in degree from modifying circumstances, and in this way that varieties are formed, and wonderfully adapted to the circumstances in which they are placed; that these variations are trans- mitted to the offspring; that many changes in plants and in animals can be produced at the will of man by altering the condi- tions of life; that some varieties are more permanent than others, and the sur- roundings of particular animals or plants may be so altered, that they fail to comply with the necessities of life and the animals or plants then cease to exist. There may indeed be a struggle for existence, and a survival of those which can live under ex- isting conditions; but, all these modifica- tions do not prove that animals in their