Access controller in side another controller

Hi

i want to access controller inside another controller
same as given in below link
http://www.techsirius.com/2013/01/load-c...other.html
its works in ci2.2

but in ci 3
when i do the above code in CI 3 mention in url page gives error

Unable to locate the specified class: Session.php

I want to access controller using uri and same controller as a object in another controller.

Thanks.