Macrophotograph of a 14.5 day old foetus of a rat still linked to the placenta (upper centre). The placenta is firmly attached to the uterine epithelium and is connected to the foetus through the umbilical cord. This is visible here as a red, narrow tubule at centre. Through the placenta oxygen is transferred from the mother's circulation into the circulation of the foetus. The placenta also conveys nutrients from the mother to the foetus. The embryo attaches to the uterine epihelium about 5 days after ovulation and the pregnancy lasts roughly 22 days. Magnification unknown.