What is the significance of the turtle?

The turtle actually symbolizes the Joad family, and their refusal to give up........ even after they get knocked down. The turtle makes us laugh, and he reminds us of the little engine that could. Like the Joads, the turtle is the epitome of a stubborn, never say die being. He just keeps going, and whn someone knocks him off his path......... he just gets up and starts over again.