The effect of moving focus graph on left and right by jQuery

$(function () {
  var _speed = 1000;
  var _len = 0;
  var _size = 150;
  var _direction = 'left';
  function mar(){
    if(_direction == 'left'){
      if(_len >= 450){
       _direction = 'right';
      }else{
       $(".flow ul").animate({"margin-left":"-=" + _size + "px"});
       _len += _size;
      }
    }else{
      if(_len <= 0){
       _direction = 'left';
      }else{
       $(".flow ul").animate({"margin-left":"+=" + _size + "px"});
       _len -= _size;
      }
    }
  }
  var _go = setInterval(mar,_speed);
  $("#pic_left").click(function (){
   _direction = 'left';
  });
  $("#pic_right").click(function (){
   _direction = 'right';
  });
  $(".flow li").mouseover(function (){
    clearInterval(_go);
  }).mouseout(function (){
    _go = setInterval(mar,_speed);
  });
});

<div class="salebox">
  <A class="left" >left</A>
  <DIV class="pcont" >
    <DIV class="ScrCont">
      <div class="flowbox" style="width:150px; height:60px; overflow:hidden;float:left;">
        <div class="flow" style="width:150px;height:60px;">
          <ul >
           <li><img src="__PUBLIC__/images/demo/" mce_src="__PUBLIC__/images/demo/" width="150px" height="60px"></li>
           <li><img src="__PUBLIC__/images/demo/" mce_src="__PUBLIC__/images/demo/" width="150px" height="60px"></li>
           <li><img src="__PUBLIC__/images/demo/" mce_src="__PUBLIC__/images/demo/" width="150px" height="60px"></li>
           <li><img src="__PUBLIC__/images/demo/" mce_src="__PUBLIC__/images/demo/" width="150px" height="60px"></li>
          </ul>
        </div>
      </div>
    </DIV>
   </DIV>
  <A class="right" >right</A>
</div>