PHP - Can Someone Please Help Me With Few Definition

I have this as my autoloader. All the classes are based off of Class O. I wanted to be able to do something like $dog = new Dog(); even if I hadn't yet created Dog.class.php and made it extend O. (I realize there are plenty of reasons this is a bad idea, this is a temporary part of the project, I am just trying to get a few things set up and thought it would work - now I'm probably going to spend more time trying to do this than it would have saved, but I'm curious. )

( ! ) Parse error: syntax error, unexpected T_VARIABLE, expecting T_STRING in C:\wamp\www\project\index.php on line 22
(line 22 is Class $class_name extends O{

Code: [Select]
<?php
function autoload($class_name) {
if(file_exists($class_name.'.class.php')){
require_once($class_name.'.class.php');
}else{
Class $class_name extends O{
}
}
}
?>
Is it possible to do what I'm trying to do?