Changes within the queen as she matured, the biological norm that we are used to, slowly developed into a human reproductive system as time went on.
As Gedimen said near the end 'there are no eggs only her womb, that is Ripleys gift to her, and now she's giving birth for you'
I know that's not the exact correct comment he makes but it's along those lines....
www.thorndesigns.netdarkness of acheronBugRenders