A histological study of the eyes of juvenile sockeye, coho, pink and chum salmon in fresh water shows that the cones, external nuclear and plexiform layers of the retinae of embryos and alevins are poorly differentiated and do not attain normal: histological or phsyiological proportions until the emergence of fry from the gravel. From a histo-physiological study it is evident that only the emerged fry and older stages are capable of '. retinomotor responses and that these become more marked

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... age. Differences in rates of adaption are found among the species and stages. Generally, the pigment layer shows a latent period before contraction in dark. Sensitivity to light is independent of the complete light-adaption of the retinal pigment or visual cells, while full acuity of vision is dependent upon the complete light-adaption of cones. Threshhold value of cones and rods are indicated by the feeding and schooling responses. At light intensities between the cone and rod thresholds the thicknesses of pigment and cone layers obey the Weber-Fechner Law. There is no diurnal rhythm in the positions of retinal pigment and cones of juvenile Oncorhyncbus either under constant light or dark. Results are discussed in relation to the migratory, schooling and feeding behaviour. The rapid downstream migration of juvenile salmon during a relative short period in the night may be related to a semi-dark adapted state of the eye. PUBLICATION Ali, M. A. Additions to the Sponge Fauna of Madras. J. Madras Univ. B., 26(2): 1956. Ali, M. A. Development of the Monaxonid Sponge, Lissodendoryx similis Thiele. J. Madras Univ. B;, 26(3): 1957. Ali, M. A. and J. R. Brett. The Structure and Photomechanical Responses of the Pacific Salmon Retina. J. Fish.Res. Bd. Canada 15 (in press) 1958.