why array_pop() used in this code?

<?
                    $slides =array();
                    //$filePath='directorypath/';
                    $dir = opendir($directory1);
                     while ($file = readdir($dir)) {
                      if (eregi("\.png",$file) || eregi("\.jpg",$file) || eregi("\.gif",$file) ) {
                      $slides[] = $file;

                      }
                       }

                       while (sizeof($slides) != 0 ){

                         $img = array_pop($slides);
                        echo '<li>';
                        echo "<img src='$directory1/$img'  />";

                          }


                       ?>