DIURNAL CHANGES IN THE ELECTRICAL RESPONSE OF THE COMPOUND EYE 1 THEODORE LOUIS JAHN AND FREDERICK CRESCITELLI (From the Zoological Laboratories, State University of Iowa} Diurnal changes in the physical environment have resulted in the establishment of biological diurnal rhythms in a large number of or-ganisms. Many of these biological rhythms are apparently under the direct control of the environment for they disappear as soon as the or-ganism is subjected to a constant environment. Others, however, ap-pear to be inherent rhythms for they continue for long periods of time after the organism is placed in a constant environment. Welsh (1938), in his review of the rather extensive literature on this subject, has cited numerous examples of persistent diurnal rhythms and has discussed the possible mechanisms that might be involved in the control of such rhythms. While engaged in a study of the electrical potentials associated with illumination of the compound eye of certain arthropods, the authors made the interesting observation that the magnitude and form of the electrical response from the eye of the carabid beetle, Chlaenius diffinis, vary according to the time of day, even though the animal was kept con-tinuously in the dark. Further investigation disclosed that such daily changes in the potentials from the eyes occurred in a number of other beetles. It is the purpose of this report to describe these diurnal fluctua-tions in potential and to correlate them with other types of diurnal changes that are known to occur in the eyes of certain invertebrates. MATERIALS AND METHODS For this investigation the following beetles were employed : Chlaenius diffinis, Chlaenius tomentosus, Hydrus triangularis, Harpalus pennsyl-vanicus, Harpalus caliginosus, Anoinoglossus etnarginatis, Osinoderina eremicola, and Necrophorus orbicollis. 2 A number of experiments were also performed with the crayfish, Cambarus virilis. All these animals were obtained directly from the field and, with few exceptions, were 1 Aided by a grant from the Rockefeller Foundation for work in Cellular Physiology. 2 The authors are indebted to Prof. H. E. Jaques of Iowa Wesleyan College for the identification of these beetles. 42
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