[4] See his classical work, “The Formation of Vegetable Mould Through
the Action of Worms, with Observations on Their Habits,” New York, 1883.
[5] Cf. Morgan. Prof. C. L., “Animal Life and Intelligence,” 1891;
“Habit and Instinct,” 1896; “Animal Behavior,” 1900.
[6] Shipley and MacBride, “Zoology,” 4th Ed., 1920.