Egg-oviduct interaction initiates reproductive behavior.

The experiments reported in this paper provide evidence that eggs must pass through the oviducts in order for receptivity to occur after ovulation in the female frog, Rana pipiens. In one experiment, oviductectomized frogs remained unreceptive after ovulation was induced by administration of exogenous pituitary glands, while sham-operates became receptive within 48 hr. Another experiment had four groups of subjects: ovariectomized females, females with oviducts ligated at the ostial end, females with openings in the uteri that prevented eggs from accumulating there, and sham-operated females. Only the last two groups, groups in which eggs could pass through the oviducts, became receptive. In these experiments, receptivity was indicated by absence of the release call during manual clasping of the trunk. Earlier experiments have shown that eggs have to pass through the oviducts in order to become fertilizable. Thus, the passage of eggs through the oviducts provides a mechanism which links the onset of reproductive behavior to the availability of fertilizable gametes.