Asks whether he may use CD’s letters in his work [Die natürlichen Existenzbedingungen der Thiere (1880)] in order to show that Moritz Wagner has misrepresented CD’s views.

Discusses the influence of isolation and external conditions on animals, and the relative importance of the direct effect of external conditions and of selection in bringing about change.

Gives CGS permission to use his letters in any way he thinks fit.

Discusses the direct effect of external conditions as an agent of change in organisms; has encountered many cases since the publication of Origin.