Part 16 · Chapter 109

And there is another reason: for the rest of the Mochin are for the need of the person himself, but from the third brain, of the Hesed and Gevura, issues the drop of semen, to beget other offspring. For the Hesed and Gevura are called "the son and the daughter" (Bra u-Barta). Therefore the drop of semen — of the male it is from the aspect of the Hassadim alone, and of the female, from the drop of the Gevurot alone — and from these alone is the building of the body of the offspring.