Sends his paper on locusts ["Die geographische Verbreitung der Wanderheuschrecke", Petermann’s Geogr. Mittheil. (1871)]. The effect of the growth of forest land on their increase; meteorological and climatic effects.

Also observations made on increase in mice as a result of increase of locusts, on whose eggs they fed, and of increase of weasels that fed on mice.

Calls CD’s attention to a book that deals with subjects related to both Descent and Expression: Ferdinand Jahn, Die abnormen Zustände des menschlichen Lebens als Nachbildungen und Wiederholungen normaler Zustände des Thierlebens [1842].