process of fecundation and generation, which theretofore had been wrapped in the deepest obscurity. Four years later, in 1848, followed Du Bois-Reymond's researches in animal electricity and the roof that the nerve is not, as formerly believed, a mere conductor, but a self-generator of the electricity originated by chemical metabolism and the transformation of what is designated as potential force or elasticity into living force or motion by virtue of the great principle of the conservation of force.
Under the head of physiology, special mention must also be made of the great successes that accompanied the researches of Messrs. Schiff, Ferrier, Munk, Nothnagel, Hitzig, Fritsch, Broca, Flechsig, and others concerning the localization of the various activities of the soul, or the divisions of labor taking place in the brain, and the topographical distribution of certain functions of the brain on its surface—researches which have not by any means reached their end. The most important among these is the discovery, made first by Broca, in 1861, of the controlling center of speech at a definite place in the fore part of the brain. Morbid degeneration or destruction of this spot is the cause of aphasia, or speechlessness. This discovery also satisfactorily explains why the large manlike apes which are almost devoid of that part of the brain can not speak, notwithstanding the formation of their larynges is similar to that of man. Not less important are the entirely new researches of Professor Flechsig on the so-called centers of association in the brain and the definite proof furnished by him that all thinking springs from the senses, inasmuch as it is only by the gradual development of those centers that the action of the different organs is connected, and thus thinking and intelligence are made possible.
Zoölogy.—Besides the numerous acquisitions of systematic zoölogy, special mention should be made here of the researches as to the life in the sea. These have been prosecuted largely through the zoological marine stations supported by Government, and have been rendered more effective by means of improved apparatus which made possible the acquisition of knowledge as to the deep-sea fauna. The results enabled Haeckel to establish his renowned Gastræa theory, according to which all animal species—however far differentiated—owe their primal origin to a single primitive form of the greatest simplicity that might be properly designated as "primitive stomach." To the zoölogical researches of the century we are also indebted for the better knowledge of those strange animal creatures nearest to man whose existence was still doubted or relegated to the realm of fable as late as the last century even by scholars, although as early as 500 b. c. the Carthaginian Hanno had seen gorillas on the western coast of Africa, and described them as wild "haired men."