Page:Popular Science Monthly Volume 31.djvu/532

516 Russel Wallace, whose masterly works on the "Geographical Distribution of Animals," and on "Island Life," have immense geological as well as biological implications.

In pure biology, besides the grand advance implied in the establishment of the doctrine of descent with modification, and its subsidiary principles of survival of the fittest and sexual selection, profoundly important minor results have also been attained in many directions. Embryology in the hands of Von Baer and his successors, notably Kowalevsky and Balfour, has acquired prime importance as an instrument of geological research. Comparative osteology in the hands of Owen, Huxley, Gaudry, and Busk has given us new views of the relationships between vertebrate animals. The pedigree of fishes, amphibians, reptiles, birds, and mammals has been worked out with a considerable degree of fullness from the hints supplied us by the amphioxus, the ascidian larva, the facts of embryology, and the numerous recent discoveries of intermediate or arrested organisms, recent and extinct. Invertebrate zoölogy has been rescued from chaos and partially reduced to temporary and uncertain order. Botany, at once the dullest and the most alluring of all sciences, has been redeemed from the vicious circle of mere classificatory schemes, and vivified by the fresh and quickening breath of the evolutionary spirit. The new morphology has revolutionized our ideas of vegetal homologies; the new physiology has fastened all its attention on the adaptations of the plant to its natural environment. The fascinating study of the mutual relations between flower and insect in particular, set on foot before the dawn of our epoch by Christian Sprengel, but reintroduced to notice in recent times by Darwin's works on orchids and on cross-fertilization, has been followed out with ardor to marvelous results by Hermann Müller, Axel, Delpino, Hildebrand, Lubbock, Ogle, and others. Heer and Saporta have worked out in great detail the development of several fossil floras. Last of all, Herbert Spencer has cast the dry light of his great organizing and generalizing intelligence on the problems of heredity, genesis, variation, individuality, and the laws of multiplication. Fifty years ago biology was a mighty maze wholly without a plan. To-day the clew has been found to all its main avenues, and even the keys of its minor recesses are for the most part well within reach of the enlightened observer.

Even the actual gains in the number of new organisms added to our lists during the last half-century are in themselves astonishing; and, strange to say, the species that bear most closely upon the theory of organic evolution are almost all of them quite recent additions to our stock of knowledge. The gorilla appeared on the scene at the critical moment for the "Descent of Man." Just on the stroke when they were most needed, connecting links, both fossil and living, turned up in abundance between fish and amphibians, amphibians and reptiles, reptiles and birds, birds and mammals, and all of these together