Rescue rat with protruding penis

Question
Hi there,
I run a rat rescue, and I have seen many things over the years, but this is something I've never seen before.  I received four baby boy rats today.  One of them has a protruding penis.  It doesn't look swollen, irritated, crusty or anything.  It just well... sticks out... really far.  I've done all kinds of searching, and read through all my books and I can't find anything!

He is of course going to the vet tomorrow morning, but I am hoping to find some kind of insight on the subject.  He's an otherwise healthy little guy considering the conditions he was living.
Thanks a lot!

Answer
It's called prolapsing. Honestly, I have NO idea why young boys can have this happen; however I recently had a litter with 3 boys prolapsed from birth onward. They're healthy and happy; and I still can't figure out why or how to correct it.

So if you find out, PLEASE enlighten me! It's something I need to learn on as well!