1. Temperature dependence of the conduction velocity and the duration of the rising and falling phase of action potential was studied in the median and lateral giant fibres of the nerve cord of earthworms acclimated to 13° or 23° C.
2. Compensatory acclimation of the conduction velocity was found at all temperatures studied from 6° to 32° C. However, the effect was statistically significant only at 6° C.
3. The temperature coefficient (Q10) of the conduction velocity was lower at all temperatures for the cold-acclimated animals. The difference was significant only for the temperature interval from 6° to 13° C.
4. The compensatory acclimation of the duration of the rising and falling phases of the spike was statistically significant at 6° and 13° C. The corresponding Q10 values were lower for the cold-acclimated animals.
5. The duration of the falling phase of the action potential showed the most efficient compensatory acclimation of the parameters studied.