Thanks MW for his essay [Die Darwin’sche Theorie und das Migrationsgesetz der Organismen (1868)]. Is highly gratified that MW agrees with him to a considerable extent.

Almost wishes that he could believe in the importance of isolation to the same extent as MW.

Comments on essays by MW [Das Ausland, May 1875]. Criticises his theory of isolation as source of species change: "But my strongest objection to your theory is that it does not explain the manifold adaptations in structure in every organic being". Believes MW has misunderstood his views: "I believe that all the individuals of a species can be slowly modified within the same district … I do not believe that one species will give birth to two or more new species, as long as they are mingled together within the same district."