Problem with use of .parents()

Problem with use of .parents()

I've the following situation

<table>
 <tbody>
   <tr>
    <td>
           <table>
              <tbody>
                 <tr>
                      <td><a class=little></a></td>
                 </tr>
                 <tr>
                      <td><a class=little></a></td>
                 </tr>
             </tbody>
           </table>
    </td>
    <td>
           <table>
              <tbody>
                 <tr>
                      <td><a class=little></a></td>
                 </tr>
                 <tr>
                      <td><a class=little></a></td>
                 </tr>
             </tbody>
           </table>
    </td>
  </tr>
 </tbody>
</table>

I'd like to set the highlighted tables' opacity to 0.8 using .parents() on $("a.little").

While the following code is working fine...

<script>
    $(function() {
        var littlobj= $("a.little");
        littlobj.each(function (){
                 $(this).parents().eq(3).css('opacity', '0.8');
                                       });
                    });
</script>  

...this code doesn't work:
 
<script>
    $(function() {
        var littlobj= $("a.little");
         //
        littlobj.parents().eq(3).css('opacity', '0.8');
        //
    });
</script>   

Why is this second code wrong? What's the difference between the firs and the second form?
Thanks,
Fabio.