1. The absence of the nares in either the male or the female South African clawed toad, or simultaneously in both partners of injected pairs of animals does not interfere in any way with the correct orientation of the male in the adoption of the normal lumbar embrace during coupling.

2. The mating reflex occurred spontaneously in Rana temporaria at the time of the breeding season under captive conditions in 70 per cent. of the animals observed. This reflex was completely inhibited in pairs of animals which had the anterior lobes of their pituitaries removed before the breeding season in both the males and the females (23 pairs); in the males only (10 pairs); or in the females only (10 pairs).

3. Oviposition did not occur regularly in the control animals which mated in the laboratory. The eggs laid were not always fertilized. Fertilized eggs were not viable for more than 2 or 3 days.

4. Removal of the gonads in both the males and the females (28 pairs of Rana) before the breeding season completely inhibited the mating reflex in these animals during the breeding season.

5. Injection of active anterior pituitary extracts into South African clawed toads previously hypophysectomized (anterior lobe alone or both lobes) elicited the normal mating reflex after the normal post-injection interval.

6. Injection of these extracts into gonadectomized clawed toads, or toads with gonadal hypofunction, failed to elicit the mating reflex.

7. Evidence is considered in support of the hypothesis that the pituitary gonadal relation involved in the act of mating is a hormonal one.

1851 Exhibition Science Research Scholar.