Clio:~ kev$ irb
>> class Foo; end
=> nil
>> class Bar < Foo; end
=> nil
>> class Baz < Foo; end
=> nil
>> ObjectSpace.each_object(Class) {|c| puts "Subclass of Foo: #{c.inspect}" if c < Foo }
Subclass of Foo: Baz
Subclass of Foo: Bar
=> 400
>>