*bows* Well, oddly enough, I had a little bit of dialogue written up with the intention of someday actually using it to explain a bit about what goes on down there, but I don't think I will. Basically, it went like this:
Veronica: So… wait. Your armor is your skin?
Bill: Yes.
Veronica: Huh. I always thought you were just wearing something. You know. Like a hitmonchan.
Bill: No, I do believe this is my skin.
Veronica: So… all this time, you've been naked?
Bill: …Yes.
[There's a small bit of silence here.]
Veronica: …I don't mean to ask questions I shouldn't be asking, Bill, but, uh…
Bill: It's covered by a pelvic plate, Veronica.
Veronica: I was about to ask you if you felt cold, pervert.
(Or, alternatively, males have retractable tubes. Females... I dunno. They lay eggs, though.)