Broad limits to functional reproductive activity seem to be set by the photoperiod—neuroendocrine system.
These captives had been kept for several months at a temperature of 21 degrees Centigrade, and on a daily photoperiod of 15 hours.
In general, Tb's showed a marked circadian cycle in phase with photoperiod.
The mice were kept in a room in which temperature and photoperiod were controlled.
photoperiod pho·to·pe·ri·od (fō'tō-pĭr'ē-əd)
The duration of an organism's daily exposure to light, considered especially with regard to the effect of such exposure on growth and development.