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-continue>
    <alltransclusions gatcontinue="千年村|18" />
  </query-continue>
  <query>
    <pages>
      <page pageid="8" ns="0" title="羽茂郡菅生郷(新潟県)" />
      <page pageid="9" ns="0" title="加茂郡久知郷(新潟県)" />
      <page pageid="10" ns="0" title="蒲原郡勇礼（いくれ）郷(新潟県)" />
      <page pageid="11" ns="0" title="雑太郡八多郷(新潟県)" />
      <page pageid="12" ns="0" title="羽茂郡大目郷(新潟県)" />
      <page pageid="13" ns="0" title="頸城郡栗原郷(新潟県)" />
      <page pageid="14" ns="0" title="古志郡文原郷(新潟県)" />
      <page pageid="15" ns="0" title="雑太郡岡郷(新潟県)" />
      <page pageid="16" ns="0" title="頸城郡都有郷(新潟県)" />
      <page pageid="17" ns="0" title="羽茂郡駄大郷(新潟県)" />
    </pages>
  </query>
</api>