Riddles, elephant jokes, rhymes, knock-knocks. . . if you've heard it three times it's here. But perhaps that merely testifies to the durability of the selections? At any rate children who haven't yet heard them will find here a fuller and more varied collection (99 items in all) than in many recent juvenile joke books. And for variety you can always ask the riddles backwards, beginning with the answers: Moby Grape. . . His powder puff is on the wrong end. . . By the footrpints in the jello. . . .