Labels:bulletin board | dialog box | sky | web site | window OCR: Stages anr Events Early Human Prenatal Development Stage Time Period Principal Events 12-24 hours following Oocyte fertilized zygote has 23 pairs of ovulation chromosomes and genetically distinct 30 hours tO third Kep Mitosis increases cell number Third to fourth day Solid ball o cells Fifth day through Hollowed ball forms trophoblast (outside) second week and inner cell mass, which implants and flattens form embryonic disc End of second week Primary germ layers form
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