During this period, embryology shifted toward growing embryos and embryonic cells outside their native environments, enabling controlled experimentation. Practical in vitro culture systems emerged, including surface-supported chick embryo culture on membranes with defined media, which supported early vascularization-like development and cross-species comparisons. Mammalian embryo culture advanced to the two-cell to blastocyst stage outside the uterus, and the establishment of long-term cell lines began to transform research into a cell-biological discipline.