$(document).ready( function() {
    $(".maproll").each(
      function(){ 
        $(this).hover(
          function(){ 
            var srcValue = $(this).children().children().attr("src");
            var newSrcValue = srcValue.replace("\.png","_on\.png");
            $(this).children().children().attr("src",newSrcValue);
          },
          function(){ 
            var srcValue = $(this).children().children().attr("src");
            var newSrcValue = srcValue.replace("_on\.png","\.png");
            $(this).children().children().attr("src",newSrcValue);
          }) 
        });
      });