This paper describes time-lapse cinematography on cattle blastocysts hatching from the zona in vitro. Four normal morulae were taken on Day 6 and cultured for 5 days. During this period 3 formed normal blastocysts of which 2 hatched from the zona without undergoing any contractions. Early blastocysts were taken on Day 7, frozen and stored at low temperature. After thawing they were cultured; only 1 of the 11 behaved like the normal embryos, and the others underwent contractions and failed to hatch. These contractions could be interpreted as a sign of an alteration of the trophoblastic structure and properties.
Cell division was observed in intact and dissociated mouse embryos between the 2-cell stage and the blastocyst in embryos developing in culture. Division to the 4-cell stage was usually asynchronous. The first cell to divide to the 4-cell stage produced descendants which tended to divide ahead of those cells produced by its slow partner at all subsequent stages of development up to the blastocyte stage. The descendants of the first cell to divide to the 4-cell stage did not subsequently have short cell cycles. The first cell or last cell to divide from the 4-cell stage was labelled with tritiated thymidine. The embryo was reassembled, and it was found that the first pair of cells to reach the 8-cell stage contributed disproportionately more descendants to the ICM when compared with the last cell to divide to the 8-cell stage.
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