Thanks for answering--I was beginning to think I'd grossed everyone out!

He's a shelter dog, and his papers said he was neutered. He's now 7 years old, so I imagine it was done some time ago. I would say he "acts" like a neutered dog--he's very territorial in the home, but if a poodle barks at him he whines.

I've only had him since last October but have never seen his testicles before this; they appeared and disappeared very quickly. But they felt very hard, which makes me think SOMETHING is there!

Thanks for the advice; I'll give the vet a call.