Page:Evolution of Life (Henry Cadwalader Chapman, 1873).djvu/173



study of the transitional stages through which plants and animals pass from the early to the mature condition is not only of immense importance to the Physiologist, but equally so to the Zoologist, Botanist, and Geologist. Notwithstanding that some knowledge, at least, of Embryology is demanded in the study of Biology, the subject is comparatively little cultivated, owing, probably, to the limited means of obtaining material, and the difficult manipulation required in this kind of work. Nevertheless, since 1759, the year in which Wolff published his "Theoria Generationis" there have appeared from time to time Embryologists like Von Baer, Schleiden, Schwann, Coste, Remak, Rathke, etc., who, after overcoming the difficulties inherent to the nature of their studies, left treatises which will always be models of scientific work and philosophic thought. Our prescribed limits only permit of briefly calling attention to some of the conclusions of Embryology, pointing out the manner in which they confirm the theory of the evolution of life as deduced from the structure and petrified remains of the vegetal and animal kingdoms. Those who are ignorant of the early stages of plants and animals will hardly believe that beings so different as sea-weed, oaks, star-fishes, mollusca, guinea-pigs, rabbits, dogs, and men begin their life in the same way; yet Fig. 160 represents equally well the cell, or primitive stage, of any of the plants or animals just mentioned. Confining ourselves for (125)