I've been wondering that for years. I remember when I first saw it I was saying, "Okay, Tippy's a boy, No wait! He's a girl! Oh I don't know!" Correct me if I'm wrong but, I do recall Tippy's mother saying to both Tippy and Spike, "Come on boy's, lets go home." Notice the word BOY in there. So, I've come to the conclusion that Tippy, is in fact, a boy.