We measured an electric potential on the body surface of a silkworm at different environmental temperatures, considering the relationship between the electric potential and the contraction of the silkworm's dorsal vessel. There was a strong relation between the two. There existed small oscillations in the contractile movement of the dorsal vessel with larger roughly periodical fluctuations, especially in its expansion period. The number of oscillations gradually decreased as the temperature rose. The expansion period of the dorsal vessel was about two times longer than the contraction period on average at every temperature and both periods decreased when the temperature rose. The contractile movement was more stable at temperatures ranging between 24.3℃ and 25.6℃.
