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