Actually Akira Toriyama stated in a interview for Shonen Jump that the Namekians are a hermaphroditic race as opposed to asexual with physiques/qualities most similar to those of human males. I assume this would mean the ‘female’ organs are inside as opposed to the opposite. As he is the creator, I don’t think there’s much argument there to offer. (Regardless what Team Four Star says *lol* ) In a lot of ways this actually makes the most sense as the Nameks are based on slugs and snails, and slugs are in fact all hermaphrodite and reproduce by eggs.