call service from another service

Question

i am trying to follow the Layered service Model http://2.bp.blogspot.com/_Ulehi1qz3j0/SDFTyiUkRGI/AAAAAAAAACc/J0UiCKTeKQk/s1600-h/Layered+Service+Model.gif , so Process service should call task service or entity service. now i just instantiate the other service from first one as class instantiation Service2 myOtherService = new Service2(). i know it is wrong, but should i add service reference in service project and call the other service through proxy as i do in web client? thanks in Advance