ABSTRACT
Throughout the normal reproductive cycle in Xenopus laevis the serum calcium level is higher in females than in males.
The reproductive cycle in females is associated with changes in the serum calcium level and in ovarian activity. In male toads the serum calcium remains remarkably constant except for a slight rise during the breeding season.
Captivity first causes a rise and then a steady decline in the serum calcium level of females. Both phases are accompanied by a progressive involution of the ovaries. The serum calcium of males is unaffected by captivity.
It is suggested that seasonal variations in the amount of solar radiation and inadequate illumination during captivity are the main agencies influencing serum calcium (through the pituitary and parathyroid glands) and ovarian activity (through the anterior lobe of the pituitary).
