Bava Batra 127: When Is a Male Not Male? When Is a First-born Not First-Born?

How the laws pertaining to a "Tumtum" affect his ability to inherit the double portion. This status has all kinds of implications to other areas of halakhah that pertain to males -- including the timing of brit milah, including the impurity that attaches to a mother after giving birth. Also, a question was sent to Shmuel: When a person has knowledge that he is the first-born, and his father says that someone else is the first-born -- does the father's statement hold sway or not? (it's a machloket)