An uneven dozen of "Fantasy and Science Fiction Tales About Humans Who Can Change Their Shapes." As most of the stories depend on the shock of the switch, they tend in the aggregate to cancel each other's effectiveness. The stronger entries include an old-fashioned "Sailor Boy's Tale" by Isak Dinesen, a well-made werewolf story by Saki, and Donald Hall's more everyday fantasy about a boy who finds himself trapped within his "Wonderful Dog Suit." Like Manley and Lewis (above), Yolen prefaces each selection with notes of her own. These bits of lore blend easily with the more conventional stories, but her items on the cockroach, for example, are ludicrously irrelevant to Kafka's "Metamorphosis"--a story which, in any case, belongs in a different league entirely. Not the most fortuitous coming together, even though piece by piece Yolen's selections reflect a classier taste than do those in Nature's Revenge.