Niddah 28: Androgynos and Tumtum Offspring

After discussing the status of a woman who does not give birth but who's offspring shows his/her hand and then pulls it back, we turn to a new and important Mishna.  We learn that a woman might give birth to a child that is neither male nor female.  It might be an androgynos, one with both male and female genitalia, or a tumtum, one whose genitals are covered or hidden.  

Both are considered to be both male and female, where the mother is ritually impure due to childbirth for fourteen days like after having had a girl and any blood that she sees is ritually pure until forty days after birth, like having a having had a boy.  The Mishna considers the status of a woman who gives birth to twins: a tumtum and a female; an androgynos and a boy.  Then it mentions offspring who are born in pieces, who are born breech, and who are born with most of the head (to the forehead) first.

The Gemara discusses many issues, including whether or not those who are androgynos and those who are tumtum are included when the Torah mentions men and women.  Are these people included when we mention other sexes or are they their own genders?  How would this be proven?  The Gemara begins to examine valuation based on sex/gender.