Is it a fish? Is it an amphibian?

We went over to Ben's house today to show the children his pond. They loved the koi in the big pond, but were even more impressed with the assorted wildlife in the smaller one. Using a jam jar, Daddy managed to catch tadpoles in several different stages of developement, so they got to see a regular tadpole, a tadpole with small back legs, a tadpole with big back legs and small front legs, and a tiny frog with a vestigal tail, all in the same jar.