In its general character the progress of natural science has been, and still is, a crusade against superstition; and it may be remarked in passing that "the nature of superstition consists in a gross misunderstanding of the causes of natural phenomena." The struggle has been more marked in biology than in other departments of science because biology involves the consideration of living organisms and undertakes to establish the same basis for thinking about the organization of the human body as about the rest of the animal series. The first triumph of the scientific method was the overthrow of authority as a means of ascertaining truth and substituting therefor the method of observation and experiment. This carries us back to the days of Vesalius and Harvey, before the framework of biology was reared. But the scientific method, once established, led on gradually to a belief in the constancy of nature and in the prevalence of universal laws in the production of all phenomena. In its progress biology has exhibited three phases which more or less overlap: The first was the descriptive phase, in which the obvious features of animals and plants were merely described; the descriptive was supplemented by the comparative method; this in due course by the experimental method, or the study of the processes that take place in organisms. Thus, description, comparison, and experiment represent the great phases of biological development. The Notable Books of Biology and their Authors.--The progress of biology has been owing to the efforts of men of very human qualities, yet each with some special distinguishing feature of eminence. Certain of their publications are the mile-stones of the way. It may be worth while, therefore, in a brief recapitulation to name the books of widest general influence in the progress of biology. Only those publications will be mentioned that have formed the starting-point of some new movement, or have laid the foundation of some new theory. Beginning with the revival of learning, the books of Vesalius, _De Corporis Humani Fabrica_ (1543), and Harvey, _De Motu Cordis et Sanguinis_ (1628), laid the foundations of scientific method in biology. The pioneer researches of Malpighi on the minute anatomy of plants and animals, and on the development of the chick, best represent the progress of investigation between Harvey and Linnæus. The three contributions referred to are those on the _Anatomy of Plants_ (_Anatome Plantarum_, 1675-1679); on the _Anatomy of the Silkworm_ (_De Bombyce_, 1669); and on the _Development of the Chick_ (_De Formatione Pulli in Ovo_ and _De Ovo Incubato_, both 1672). We then pass to the _Systema Naturæ_ (twelve editions, 1735-1768) of Linnæus, a work that had such wide influence in stimulating activity in systematic botany and zoölogy.