opinion of the palaeontological studies of Vlad. Kovalevsky and appreciated the zoological investigations of his brother Alex. Kovalevsky on the lowest vertebrates and invertebrates and on their genetical relationship. His works, as well as the works of Metchnikov, were in the main directed to establish unity of organization in animals.
The theory of evolution was, however, eventually modified by the subsequent doctrine of "heterogenesis," formulated by the late Korzinsky: he stated that among numerous homogeneous posterity, born from normal parents, there appear suddenly separate individuals with very marked peculiarities; these variations are probably due to some internal changes, occurring in the cell of the ovum, and come after a certain period of accumulation of vital energy through a series of generations; the rare individuals subjected to them are able to transmit them, in favourable circumstances, to their descendants, forming thus a new "race"; natural selection and other factors can only strengthen these acquired characters and suppress further variations in this race.
The scientific conception of evolution provoked, moreover, some criticism in the domain of moral and historical sciences. It was formulated in a transcendent way by Solovyev; he acknowledged an Absolute Cause or a Creative Force, without which evolution is not possible; but he supposed that God's thought, which is absolute destiny in regard to things, is only a duty for a moral being. In this way he tried to solve the problem of "free will" and of man's mission, which is to realize, "in union with God," Truth, Good, and Beauty in the
