Herbert Jennings was a zoologist who contributed many behavioral studies on unicellular organisms, and especially Paramecium (the swimming neuron!). I have collected a number of his papers and books, which are in the public domain:

Books:

• Jennings (1904). Contributions to the study of the behavior of lower organisms.
• Jennings (1906). Behavior of the lower organisms.

Papers:

• Jennings (1897). Studies on Reactions to Stimuli in Unicellular Organisms- I. Reactions to Chemical, Osmotic and Mechanical Stimuli in the Ciliate Infusoria.
• Jennings (1899). The behavior of unicellular organisms.
• Jennings (1899). Studies on reactions to stimuli in unicellular organisms. II.—The mechanism of the motor reactions of paramecium.
• Jennings (1899). Studies on reactions to stimuli in unicellular organisms. III reactions to localized stimuli in spirostomum and stentor.
• Jennings (1899). Studies on reactions to stimuli in unicellular organisms. IV. Laws of chemotaxis in Paramecium.
• Jennings (1899). The Psychology of a Protozoan.
• Jennings (1900). Studies on reactions to stimuli in unicellular organisms. V. On the movements and motor reflexes of the Flagellata and Ciliata.
• Jennings (1900). Studies on Reactions to Stimuli in Unicellular Organisms. VI. On the Reactions of Chilomonas to Organic Acids.
• Jennings (1901). On the significance of the spiral swimming of organisms.
• Jennings and Crosby (1901). Studies on reactions to stimuli in unicellular organisms.—VII. The manner in which bacteria react to stimuli, especially to chemical stimuli.
• Jennings and Moore (1902). Studies on reactions to stimuli in unicellular organisms. VIII. On the reactions of Infusoria to carbonic and other acids.
• Jennings (1902). Studies on reactions to stimuli in unicellular organisms. IX.—On the behavior of fixed infusoria (Stentor and Vorticella), with special reference to the modifiability.
• Jennings and Jamieson (1902). Studies on reactions to stimuli in unicellular organisms. X. The movements and reactions of pieces of ciliate Infusoria.
• Jennings (1904). The behavior of Paramecium. Additional features and general relations.
• Jennings (1908). The Interpretation of the Behavior of the Lower Organisms.
• Jennings (1908). Heredity, variation and evolution in Protozoa. I. The fate of new structural characters in Paramecium, in connection with the problem of the inheritance of the inheritance of acquired characters in unicellular organisms.
• Jennings (1908). Heredity, variation and evolution in Protozoa. II. Heredity and variation of size and form in Paramecium, with studies of growth, environmental action and selection.
• Jennings (1909). Heredity and variation in the simplest organisms.