Figure 1.

Pineal melatonin rhythms. A. Levels of melatonin secreted by chick pinealocytes were measured for 3 days in culture under an LD cycle. White bars indicate the time when lights were on, and black bars indicate the time when lights were off. B. Melatonin levels were measured from cultured pinealocytes maintained one day of LD followed by one day of DD. Light hatched bars indicate subjective day, while dark hatched bars indicate subjective night.