post ajax data to PHP and return data

How can i post some ajax data to the controller function and get it back? For I want to post one integer to the function, and get another integer (total votes for the item which ID is posted), and on success i want to echo that vote count. I dont know how can i post the "id" to the controller function. Please see my code:

//post this integet
the_id = $(this).attr('id'); 

        $.ajax({
            type: "POST",
            data: the_id,
            url: "http://localhost/test/index.php/data/count_votes",
            success: function(){
                //the controller function count_votes returns an integer.
                //echo that with the fade in here.

                }
            });