unity 実行時 プリミティブ 生成

function Start () {
    for (var y = 0; y < 5; y++) {
        for (var x = 0; x < 5; x++) {
            var cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
            cube.AddComponent(Rigidbody);
            cube.transform.position = Vector3 (x, y, 0);
        }
    }
} 
http://docs.unity3d.com/Documentation/Manual/InstantiatingPrefabs.html