ABSTRACT
Rabbit eggs recovered from the fallopian tube during the early stages of cleavage develop readily in culture up to the late morula stage (Lewis & Gregory, 1929; Pincus, 1930; Adams, 1956; Purshottam & Pincus, 1961; Onuma, Maurer & Foote, 1968). The transition from morula to blastocyst, which normally occurs 70–76 h post coitum (p.c.) coincident with entry into the uterus, may also take place in vitro, especially if culture begins at the late morula stage. However, growth of the blastocyst is generally limited, owing to failure of expansion of the zona pellucida which may rupture (Lewis & Gregory, 1929; Pincus & Werthessen, 1938). Under certain conditions, prolonged blastocyst growth even to the preimplantation stage ‘with typical expansion and little or no herniation’ has been observed, though very few eggs were involved (Pincus & Werthessen, 1938).
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