Abstract
Summary
1. Fiddler crabs, of the species Uca pugnax, were studied with respect to their capacity to show a response of their chromatophore system to increase in showers of cosmic-ray origin obtained through the interpolation of lead screens. 2. Increasing the showers by lead screen varying from 0.3 to 2.1 cm in thickness and held 5 inches directly above the animals produced significant differences in the response of the pigmentary effector system of the crabs as compared with appropriate controls. 3. There was a strong suggestion of the existence of a diurnal rhythm in the character of the response to increasing showers. The response was increased pigment concentration or body-lightening during the initiation of transition into the day phase of the endogenous daily cycle and increased pigment-dispersion or body-darkening during at least most of the remaining hours of the day. 4. The lead screens, and distances from screen to animals, which were used were responsible for an increase in degree of darkening during the day phase in the cycle (+0.110 ±0.0195 chromatophore stage units), and for an increase in the degree of lightening during the early morning hours, (-0.142 ± 0.118 chromatophore stage units). 5. A possible functional role of this response to cosmic ray showers is discussed briefly.
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