(Mishnah - R. Yehoshua): I heard that a Seris does Chalitzah, and one does Chalitzah to his widow; and a Seris does not do Chalitzah, and one does not do Chalitzah to his widow. I cannot explain these.

R. Akiva: I will explain! A Seris Adam (castrated by man) does Chalitzah, and one does Chalitzah to his widow, because he was once able to have children. A Seris Chamah (from birth) does not do Chalitzah, and one does not do Chalitzah to his widow, since he was always sterile.

R. Eliezer: No. Rather, a Seris Chamah does Chalitzah and one does Chalitzah to his widow, because he can be cured. A Seris Adam does not do Chalitzah and one does not do Chalitzah to his widow, since he cannot be cured.

R. Yehudah ben Besira testified about a Seris Adam in Yerushalayim named Ben Megosesa. His widow did Yibum, like R. Akiva's opinion.