.next() not work for .toggle() : I using jquery function Toggle() to create a Pull down menu

But I will add many sub menu in this project.

I need th click the `a.sub_open` to toggle the `div.submenu`  

https://jsfiddle.net/mr6b4k53/

js code:

    $(document).ready(function(){
    	$( ".sub_open" ).click(function() {
    		$(".sub_menu").next.toggle("blind", 0, 500);
    	});
    });

any suggest?