A i m o f the preaerit research. Summumj of prewiowr experiments. Description of the apparatus here used; precautionor to i m r e the elimination of accidental factors as possible determinants of discrimination. Description of the method and of the order of series; system of marks; graded and percentage methods; reward and punishment ; advantages and diaadvuntages of the method. Results of the various series. Specijic efecte of the primary colours. Summary of results : A . evidence in support

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... tfre view that dogs are only able to perceive difmences of b r y h t m s s ; B. evidence in support of the view tfmt dogs possess rudimentary colowr discrimination. The effects of practice ; qualilative and quantitative improvement ; transference of improvement ; daily improvement; acl;c/mptotic character of improvement ; deterioration with practice. Retentiveness. Description of behawiour and growth of dixcrimination ; requisite conditions o f a sensory discrimination test ; nature of the mean variation in sensory discrimincltion tests on the higher vertebrates. The mgm of recognition. Iteaction types (a) aflrmative, (b) negative. Method of comparison. Position errors (a) absolute, (b) relative, forms. Self-control. Inhibition. Conditwtts sewing (a) to mask, (b) to aid, discrimination. IIabit formation and relative plasticity. T h e rSle of kinaesthetic senorations and the position songe. Individual diferences. General coiwluaions. Appendix.-Tables. These observations were made in the Cambridge Peychological Laboratory during the experimenter's tenure of a Mariou Kennedy Studentship granted by Newnham College. J. of Psych. v 9 I should here like to express my thanks to Dr Myers, under whose direction the preseut inquiry was conducted, for his suggestion of the .subject as well as of the method of experimentation, and my indebtedness to him for constant help and advice.