I've seen a number of folk art turtle stools in this manner, made in Berks County, Pennsylvania I believe, but this is the first pull toy turtle I've come across and it's a pretty fun one. (Since finding this one, I've found a few other examples sold at auction.) It looks to me like it is the original string still attached, and pulling on it sets the two wheels on the underside turning, which are attached by wires to the front and rear of the body, so the front legs and head, and hind legs and tail, move in opposite directions. Great original brown and orange paint, round headed steel nails for eyes on the angular head, and carved details around the perimeter to enhance its "shell." 

12 7/8 x 9 5/8 x 2 7/8” t and in very good condition with appropriate light surface wear.