Another matter, “when a woman conceives” – that is what is written: “You discern [zerita] my path and my resting place; You are familiar with all my ways” (Psalms 139:3). Rabbi Yoḥanan and Rabbi Shimon ben Lakish, Rabbi Yoḥanan said: The Holy One blessed be He forms a person only from a refined drop.19From the most refined part of the semen. Rabbi Yoḥanan said: Zerita, like a person who winnows and places the straw by itself and the stubble by itself, until he ensures that the grain is pure.
Rabbi Shimon ben Lakish said: Even so, he does not lose any part of the drop, but rather winnows part of the drop to [form] the brain, part of the drop to [form] the bones, and part of the drop to [form] the sinews. All the more so if it was a male. That is what is written: “When a woman conceives and bears a male child.”