Researches on the fossil remains of species of animals and plants which have been extinct for thousands and millions of years (_palæontology_) have also contributed to determine the trunk of the great tree of former life. The numerous gaps which still exist between these fragmentary documents of former ages are nevertheless too considerable for continuous connections to be established in the past by the aid of fossils. We not only know that the different forms of living beings are connected to each other by a real relationship, but we can fathom more and more deeply the degrees of this relationship, and can often prove from which group of animals a given group is descended. In many cases we can determine at which period the fauna and flora of two continents have been separated from each other, and in what manner they have been transformed, each in its own way, while still preserving the general characters which were common before their separation. The specialist can soon discover what species belong to the old geographically differentiated fauna and flora of the country, and what have been ulteriorily imported. I record these facts for the benefit of those persons who have not yet understood that it is absolutely useless at the present day to dispute the evolution of living beings. Deceived by the divergent opinions of scientists concerning hypotheses which endeavor to explain the details of evolution, these persons confound the details with the fundamental facts of evolution.