That is where they keep their 'boys' at. You can see this a lot easier if you have your guy next to it's clutch mates. Similar sized siblings will either have a bit of a bump or nothing... You can also tell a little bit by it's color vs. the color of the other siblings. This is why a breeder shipping you an animal has a better idea of who is what because they can compare them all and get a better idea.
Edit: I vote the little guy is a male. I think I see a lump.