An Odd Question

This is sort of odd, but I keep wondering about it. Why do the mice have last names (Mr. Brisby & Mr. Ages) but the rats apparently have only a single name? Any theories on that?

I've noticed that as well. I suppose there's a couple of possibilities... First, the rats might have last names, but since whenever we see them they're almost always in the confidence of friends, they might view using them as too formal. Second, they might not have them since they're more or less one large group after NIMH, without a huge need to distinguish themselves into families, while the mice that live nearby keep to their own families and thus have a family name--of course, this doesn't really explain Jonathan or Mr. Ages. Third, because Robert C. O'Brien wrote it that way. ;)

I don't really know... fun to speculate, though.