<P> The zygote contains a full complement of genetic material and develops into the embryo . Briefly , embryonic developments have four stages : the morula stage , the bastula stage , the gastrula stage , and the neurula stage . Prior to implantation , the embryo remains in a protein shell , the zona pellucida , and undergoes a series of cell divisions , called mitosis . A week after fertilization the embryo still has not grown in size , but hatches from the zona pellucida and adheres to the lining of the mother 's uterus . This induces a decidual reaction , wherein the uterine cells proliferate and surround the embryo thus causing it to become embedded within the uterine tissue . The embryo , meanwhile , proliferates and develops both into embryonic and extra-embryonic tissue , the latter forming the fetal membranes and the placenta . In humans , the embryo is referred to as a fetus in the later stages of prenatal development . The transition from embryo to fetus is arbitrarily defined as occurring 8 weeks after fertilization . In comparison to the embryo , the fetus has more recognizable external features and a set of progressively developing internal organs . A nearly identical process occurs in other species . </P>
<P> The zygote contains a full complement of genetic material and develops into the embryo . Briefly , embryonic developments have four stages : the morula stage , the bastula stage , the gastrula stage , and the neurula stage . Prior to implantation , the embryo remains in a protein shell , the zona pellucida , and undergoes a series of cell divisions , called mitosis . A week after fertilization the embryo still has not grown in size , but hatches from the zona pellucida and adheres to the lining of the mother 's uterus . This induces a decidual reaction , wherein the uterine cells proliferate and surround the embryo thus causing it to become embedded within the uterine tissue . The embryo , meanwhile , proliferates and develops both into embryonic and extra-embryonic tissue , the latter forming the fetal membranes and the placenta . In humans , the embryo is referred to as a fetus in the later stages of prenatal development . The transition from embryo to fetus is arbitrarily defined as occurring 8 weeks after fertilization . In comparison to the embryo , the fetus has more recognizable external features and a set of progressively developing internal organs . A nearly identical process occurs in other species . </P>
what are the four stages of human development
what are the four stages of human development
morula bastula gastrula neurula
morula bastula gastrula neurula