PHYLOGENY, ONTOGENY AND EMBRYO-TRANSFER

Some similarities and differences in the ways in which mammalian embryos develop up to the blastocyst stage are described and related, speculatively, to the phylogenetic position of the mammals. Particular attention is given to the farm species and to contrasts between embryogenesis in eutherian and metatherian mammals. The practical implications of these contrasts are discussed in relation to embryo manipulation and transfer. It is argued that comparative studies of mammalian embryogenesis have much to learn from, and much to contribute to, the broader field of developmental biology, and that progress in that field will expand the future applications of farm animal embryo work.