of Volume 2.- 6 The Chelicerates.- I. Introduction.- II. General Characteristics.- A. Habitat.- B. General Morphology.- C. Nervous System—General.- D. Nutrition.- E. Mating and Reproduction.- F. Respiration.- G. Sense Organs.- III. Learning Studies.- A. Habituation.- B. Conditioning.- C. Acquired Orientations.- D. Conditioning in Limulus.- IV. Conclusions.- References.- 7 Learning in Crustacea.- I. Introduction.- A. Evolutionary Relationships.- B. Early Demonstrations of Learning.- C. Reasons for Studying Crustacean Learning.- II. Characteristics of the Group Germane to Learning.- A. General Characteristics.- B. Ways of Life and Learning.- III. Features of the Nervous System Relevant to Learning.- A. General Features.- B. The Brain.- C. Neuron Numbers.- D. Ways of Economizing on Neurons.- E. Advantage of Conservation of Neurons for Studying Learning.- IV. Roles of Learning in Life.- A. Terrain and Place Learning.- B. Social Behavior.- C. Feeding Behavior and Food Preferences.- D. Sensorimotor Learning.- E. Approach and Avoidance Behavior.- F. Role of Experience During Development.- G. Hidden Learning.- H. Phases and Rhythms.- V. Formal Learning Experiments.- A. Changes in Level of Responsiveness.- B. Associative Learning.- C. Extent of Attainments.- D. Higher Mental Processes.- VI. Physiological Analysis of Learning.- A. Method 1: Raw Mechanisms and Analogues.- B. Method 2: Circuit Analysis.- C. Method 3: Holistic Procedures.- VII. Concluding Remarks.- References.- 8 Learning in Insects Except Apoidea.- I. Introduction.- II. Insect Body Plan.- III. Structure of the Insect Nervous System.- IV. Insect Evolution and Classification.- V. Insects as Subjects for Laboratory Investigations of Behavior and Neurophysiology.- VI. Habituation.- VII. Classical Conditioning.- VIII. Instrumental Conditioning: Tasks and Species.- A. Cockroaches.- B. Grain Beetles.- C. Fruit Flies.- D. Ants.- E. Wasps.- IX. “Shock Avoidance Learning” in Certain Insect Preparations.- X. Olfactory Conditioning.- XI. Processes of Learning and Memory.- A. Learning.- B. Memory.- XII. Overview and Suggestions for Future Research.- References.- 9 Honey Bees.- I. Introduction.- II. Experiments on Behavior of Bees.- III. Conclusions.- References.- 10 Learning in Gastropod Mollusks.- I. Introduction.- II. Systematic Organization.- A. Phylogenetic Relations.- B. Evolution of Nervous Systems and Anatomy.- C. Torsion.- III. Development.- A. Copulation and Egg Laying.- B. Larval Stages.- IV. Gastropod Behavior.- A. Chemical and Tactile Senses.- B. Geotaxis.- C. Vision.- D. Locomotion and Feeding Behavior.- V. Learning Studies.- A. Purely Behavioral Studies of Learning.- B. Neurophysiological Studies of Learning.- C. Correlated Behavioral Learning and Neurophysiological Studies of Habituation and Sensitization.- VI. Summary and Conclusions.- References.- Appendix (by W. H. Dall).