Developmental Failure of Swine Embryos Restricted to the Oviducal Environment

Restriction of embryos to the oviducal environment (tube-locked embryos) does not prevent embryonic development to the early blastocyst stage in mice (Kirby, 1962; Orsini & McLaren, 1967), rabbits (Pincus & Kirsch, 1956; Adams, 1958), rats (Alden, 1942) and sheep (Wintenberger-Torres, 1956), though further development of the tube-locked embryos has not been observed and they degenerate (Adams, 1958; Kirby, 1962; Orsini & McLaren, 1967). Kirby (1962) observed that mouse embryos recovered from the uterus continued to develop when transplanted beneath the kidney capsule; when tubelocked embryos were treated similarly only the trophoblast continued to develop. Kirby (1962) suggested that a `uterine factor' was required for the development of mouse embryos beyond the blastocyst stage. Recently, Krishnan & Daniel (1967) isolated a specific uterine