Pictet says, in the introduction to his "Traite de Paleontologie:" "It seems to me impossible that we should admit, as an explanation of the phenomena of successive faunas, the passage of species into one another; the limits of such transitions of species, even supposing that the lapse of a vast period of time may have given them a character of reality much greater than that which the study of existing nature leads us to suppose, are still infinitely within those differences which distinguish two successive faunas. Lastly, we can least of all account by this theory for the appearance of new _types_, to explain the introduction of which we must necessarily, in the present state of science, recur to the idea of distinct creations posterior to the first." The following are the general conclusions of Bronn, in his elaborate and most valuable essay, presented to the French Academy in 1856, as summarized in a notice of the work in the Journal of the Geological Society: "1. The first productions of this power in the oldest Neptunian strata of the earth consisted of Plants, Zoophytes, Mollusks, Crustaceans, and perhaps even Fish; the simultaneous appearance of which, therefore, contradicts the assumption that the more perfect organic forms arose out of the gradual transformation in time of the more imperfect forms. "2. The same power which produced the first organic forms has continued to operate in intensively as well as extensively increasing activity during the whole subsequent geological period, up to the final appearance of man; but here also can no traces be found of a gradual transformation of old species and genera into new; but the new have everywhere appeared as new without the co-operation of the former. "3. In the succession of the different forms of plants and animals, a certain regular course and plan is perceptible, which is quite independent of chance. While all species possess only a limited duration, and must sooner or later disappear, they make way for subsequent new ones, which not only almost always offer an equivalent, in number, organization, and duties to be performed, for those which have disappeared, but which are also generally more varied, and therefore more perfect, and always maintain an equilibrium with each other in their stage of organization, their mode of life, and functions. There always exists, therefore, a certain fixed relation between the newly arising and the disappearing forms of organic life. "4. A similar relation necessarily exists between the newly arising organic forms and the outward conditions of life which prevailed at their first appearance on the earth's surface, or at the place of their appearance.