Hard-and-fast distinctions are the marks of imperfect theory. Early philosophers distinguished hot and cold, wet and dry, light and dark, male and female, as things different in kind. In later times organic and inorganic, animal and vegetable, the activities of matter and the activities of mind, have been sharply separated. But as knowledge increases these distinctions melt away; it is perceived that the extreme cases are either now connected by insensible gradations, or else spring historically from a common root. Hutton, Lyell, and their successors have made it clear that the history of the earth calls for no agents and no assumptions beyond those that are involved in changes now going on; the present is heir by unbroken descent to the past. Continuity has been established between all forms of energy. Even the chemical elements, once the emblems of independence, give indications that they too had a common origin. The nebular hypothesis, which has been steadily rendered more probable by the scientific discoveries of two centuries, traces all that can be perceived by the senses to a homogeneous vapour, and lays the burden of proof on those who believe that continuity has its limits. Every history, whether of planetary systems, or of the earth's crust, or of human civilisations, religions, and arts, is recognised as a continuous development with progressive differentiation. Amateur Students of Living Animals. A history of biology would be incomplete which took no notice of every-day observations of the commonest forms of life. Some of the best are due to the curiosity of men with whom natural history was no more than an occasional recreation. William Turner (a preacher, who became Dean of Wells), Charles Butler (a schoolmaster), Caius and Lister (physicians), Claude Perrault (a physician and architect), Méry and Poupart (surgeons), Frisch (a schoolmaster and philologue), Lyonet (an interpreter and confidential secretary), Roesel (a miniature painter), Henry Baker (a bookseller, who gained a competence by instructing deaf mutes), Leroy (ranger to the King of France), Stephen Hales, Gilbert White and William Kirby (country parsons), and William Spence (a drysalter) were all amateurs in natural history. To this list we might add Willughby, Ray, Leeuwenhoek, Réaumur, De Geer, Buffon, the Hubers, and George Montagu, who were either so fortunate in their worldly circumstances or so devoted to science as to make it their chief, or even their sole pursuit, though they did not look to it for bread. A large proportion of the naturalists whose names have been quoted occupied themselves with the habits and instincts of animals, and biology has been notably enriched by their observations. To Englishmen the most familiar name is that of Gilbert White, in whom were combined thirst for knowledge, exactness in description, and a feeling for the poetry of nature.