Abstract
The direction of temporary phase shifts depends on the timing of the light signal in the dark period (1800-0600). Delays predominated following signals between 2100 and 2400, while advances tended, even more uniformly, to follow signals given between 0100 and 0400. In one animal the caecotrophy rhythm split into 2 components after a light signal at 0400, while in another it was so disturbed that the signal was followed by a coprostasis of 10 days. The phase responses to light stimuli of the rabbit caecotrophy rhythm correspond well with those obtained in nocturnal rodents.