Copulation takes place from June until March inclusive but is most frequent between September and November. This is also the season for oviposition, the eggs hatching the following summer. The growth curve of young tortoises shows a close correlation between body weight and length of carapace. Irregularities of the laminae are frequent. These tortoises can survive indefinitely without water if provided with succulent green food. The rate of transpiration in dry air is low: it takes place mainly through the lungs in baby animals but cutaneous transpiration accounts for about half the evaporative water-loss from older tortoises. A complete water and metabolic balance sheet has been drawn up and an analysis of urine made. Tortoises show behavioural thermoregulation and, if the body temperature reaches40–41°C, copious salivation produces evaporative cooling which prevents any further rise. Reactions to high temperatures are direct and are not mediated through responses to light intensity. There is a well marked temperature-independent circadian rhythm of activity which is neither accelerated nor retarded by constant light or darkness. Locomotion is stimulated by light and inhibited by darkness, but the phase of the rhythm is not reset by three-hour periods of light when the animals are kept in darkness not by three-hour periods of dark when they are kept in light, at whatever hour of the 24-hour cycle these changes are applied.