Abstract
1. The effect of different temperatures (8° to 24° C) upon the rate of normal development and upon the frequency of the malformation "double abdomen" in partially UV irradiated eggs ofSmittia was tested. 2. The Q10-value of the rate of normal development increased with decreasing temperature. A value of 1.8 was found between 24° and 20° C, a value of 5.4 was reached between 12° and 8° C. 3. The frequency of double abdomens in UV irradiated eggs decreased with increasing temperature on dark cultivation after UV irradiation. This effect is named "thermoreversion" 4. Dose-response curves obtained at cultivation temperatures of 8° and 20° C, respectively, show a constant dose reduction factor of 0.58. 5. Thermoreversion occurred after UV irradiation at all stages from egg deposition to formation of preblastoderm. 6. The kinetics of thermoreversion show significant, stage dependent deviations from a simple exponential rise. This finding indicates complicated interrelations between thermoreversion and developmental changes within the egg. 7. Incubation of irradiated eggs in a 50 μM NaCN solution caused a significant increase of the frequency of double abdomens. 8. Some speculations about mechanisms possibly underlying thermoreversion are presented.
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