Note 2 — INTRODUCTION
Reading edition
For an excellent discussion of this problem see Holmes, Prof. S. J., “The Evolution of Animal Intelligence,” Pages 63-89, New York, 1911; and Jennings, Prof. H. S., “Behavior of Lower Organisms,” New York, 1906. See also, Day and Bentley, “A Note on Learning in Paramœcium,” Journal of Animal Behavior, 1, 67, 1911; and Watkins, G. P., “Psychical Life in Protozoa,” American Journal of Psychology, 11, 166, 1900.