var rows = $('#mytable tbody tr').get(); 
$.each(rows, function(index, row) { 
$('#mytable').children('tbody').append(row); 
});
<table  class="sort" id="mytable"> 
<thead> 
<tr>
<th id="number">№</th>
<th id="surname">Фамилия</th>
</tr> 
</thead>
<tbody>
<tr><td>1</td><td>Иванов</td></tr> 
<tr> <td>2</td><td>Петров</td></tr> 
</tbody>
</table