Induction of ovulation by a mixture of steroids. Frogs were treated with a mixture of estradiol (E) and progesterone (P) at the indicated concentration. The left column represents induction results in response to PMSG-hCG injection. After 24 to 30 hr incubation, the numbers of ovulated eggs were counted as described in the Materials and Methods. Each value represents the mean of data from more than three different females. The number of ovulated frogs per number treated is indicated over each column. Vertical lines indicate standard deviation.