DAVID SPEARS LTD / SCIENCE PHOTO LIBRARY DAVID SPEARS LTD / SCIENCE PHOTO LIBRARY
Macrophotograph of a 15.5 day old foetus of a rat. The foetus is normally situated inside a fluid filled sac, which was here removed, known as the amniotic cavity. The fluid is mostly formed by water and protects the foetus against the pressure of the internal organs of the mother and from any injury from the mother's movements. The embryo of a rat attaches to the uterine cavity about 5 days after ovulation and the pregnancy lasts roughly 22 days. At bottom right the developing tail is clearly visible. Magnification unknown.
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