[jQuery] Re: Appending text works; appending element doesn't

[Rodent of Unusual Size]

I can't see anything I'm doing wrong here, but it still won't work.
I've tried this:

<code>
var span = $('<span>Elem</span>');
span.appendTo(this);
</code>

but then Firebug says:

<code>
Node cannot be inserted at the specified point in the hierarchy" code:
"3
  this.appendChild( elem ); [jquery.js line 238]
</code>

I'm lost here..