Breed Not Defined???

function Dog (breed) {
    this.breed = breed;
};

// add the sayHello method to the Dog class
// so all dogs now can say hello
   Dog.prototype.sayHello= function(){
        console.log("Hello this is a"+" "+breed+" "+"dog.")
    };

var yourDog = new Dog("golden retriever");
yourDog.sayHello();

var myDog = new Dog("dachshund");
myDog.sayHello();