While rubber squeak toys have been around since the 1800s, no one has identified exactly who hatched the idea of the rubber duck. Examples of yellow, molded-rubber duck toys appeared around the 1940s. Over the years, their design has evolved, settling on a standard form of a swimming duck with a bright orange bill. In more recent years, rubber ducks are not even rubber--they're mostly made of vinyl. Rubber ducks are most often identified as a bath-time plaything for babies and toddlers. Their image as the quintessential tub toy was sealed in 1970 when Ernie, the cheerful orange Muppet on "Sesame Street" sang "Rubber Duckie." The catchy song went on to become a childhood hit, in the same way that the ducks themselves had become a standard part of childhood. Simple, durable, and inexpensive, they outlasted more complex toys. The cheerful yellow quackers have become such an artifact of pleasant childhood memories and nostalgia, some manufacturers offer them in forms suited more to adult collectors than to little tykes in the tub.