Hi! Back in the late 70s / early 80s, when I was in grade school, we read a short story that I don't remember the name or author. The story may have been written in the 50s or 60s. It's set in a zoo with a father and son looking at all these unusual animals who were mutated after a nuclear war. Near the end of the story, a gorilla (I think) reaches out and tears the son's arm out of the socket. The story ends with a doctor telling the father that they can't reattach the arm, but no worries, the kid still has two arms -- the nuclear war gave humans three arms. Anybody remember the story name or author? I would like to read it again and some of the writer's other sci-fi stories.