This article or the following section is not adequately provided with supporting documents ( e.g. individual evidence ). Information without sufficient evidence could be removed soon. Please help Wikipedia by researching the information and including good evidence.
A distinction must be made between the embryoblast and the trophoblast , the part of the blastocyst from which extraembryonic tissue develops, for example the membrane and, in higher mammals , part of the placenta . In humans, the differentiation of embryonic cells into embryoblast and trophoblast takes place around the 4th day of embryonic development .