In the frog, Rana temporaria, the number of eggs in a clutch ranged from about 2500 to 9000/100g body mass and egg diameter ranged from 1.1 to 1.9 mm. There was an inverse relation between number and size of eggs. It is indicated that egg size depends upon the number of oocytes recruited to vitellogenic growth and that the number of oocytes recruited depends upon the number of small oocytes that constitutes the recruitment pool. The total amount of yolk deposited in the ovaries was independent of the number of eggs, i. e. clutch size. During an ovarian cycle, therefore, physiological mechanisms seem to regulate the amount of yolk deposited within the ovaries at large, rather than in the individual vitellogenic oocyte.