Experimental studies on the organization of the preimplantation mouse embryo

The reaggregation and subsequent development of a range of disaggregated embryos has been examined: 1. Following complete dissociation embryos from 8-cell to late blastocyst reaggregated and developed to form morphologically normal blastocysts, even when blastomeres of two different developmental stages were present in the reaggregate. 2. Dissociated mid-blastocysts could also reaggregate to form blastocysts but more commonly they produced vesiculated masses, as did disaggregates of Jate blastocysts. 3. Successful fusion of pairs of mid or late blastocysts, with full cell numbers, was achieved following partial dissociation. These results are discussed in relation to blastocyst formation. It is suggested that even if the embryo derives polarity from the oocyte it is not functionally essential to normal development in view of the remarkable regulative capacity of the egg.