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THE effect of photoperiod on the cyclic nature of eating and muscular activity of animals is generally recognized, but its effects on the physiologic activity of various organs are not fully appreciated. Tyler (1958) reported the variation in the quantity of gastrointestinal excretion that occurred in poultry and related the variations to the influence of the starting time (zero hour) and to the length of a time unit. In a study of red-winged blackbirds and starlings collected by shooting or netting, Fisher and Bartlett (1957) observed a difference in liver weight and in color of birds killed at different times during the natural daily photoperiod. While relatively small samples were used, the differences between day and night samples were significant. Changes in energy storage of fat in the liver preparatory to migration have been reported by Farner et al. (1961) and by Odum (1960). The present investigation was made to…
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Wilson et al. (1969) studied this question.
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