Niddah 31 - Cleopatra's Experiment
Rabbi Ishmael disagrees with the forty days for the formation of the fetus rule above , and says that the male forms in forty days, but the female forms in eighty days. The Sages argued with him based on Cleopatra's experiment, when two of her maidservants were sentenced to death for offense against the crown. She had them cohabit on the same day, then examined them on the forty first day: one had a male, another a female, both formed. Rabbi Ishmael answered, "I am bringing a proof from the Torah, and you are responding with a proof from imbeciles!"
What is the Torah's proof? Just as the days of the mother's purity after giving birth to a female are eighty days, so too is the formation of a fetus, while for a male it is forty days. And the Sages? They say, "You cannot compare the formation of fetus to the laws of ritual purity." What did Rabbi Ishmael answer to the experiment? He said, "Perhaps the woman with the female was pregnant from before." The Sages said, "Cleopatra appointed a guardian for her!" Rabbi Ishmael answered, "There is no guarding against promiscuity."
In a different version of the story, the positions were reversed. Rabbi Ishmael was quoting the experiment, which was reported to have eighty days for a female, and the Sages were arguing against his proof.
A lamp is lit for an unborn child in its mother's womb, and he peers and sees from one end of the world to the other. They teach him the entire Torah, but as soon as the child emerges into the world, an angel comes and strikes him on the mouth, causing him to forget it all. However, the child cannot be born until he gives an oath. They tell him to promise "Be a good person, and don't be a bad person. However, even if the whole world tells you that you are righteous, view yourself as having achieved nothing at all."
Art: Ferdinand Georg Waldmuller - The Young boy with a Lamp