You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query>
    <pages>
      <page pageid="38" ns="0" title="Why did insects won?" />
      <page pageid="87" ns="0" title="Volume of people" />
      <page pageid="99" ns="0" title="Library of hypothetical books" />
      <page pageid="114" ns="0" title="T-shirts" />
      <page pageid="143" ns="0" title="Some studies using animal testing" />
    </pages>
  </query>
</api>