[omniORB] _sk_Echo ???

[Muzero]

Hi to all,
i'm new with omniORB and general CORBA::programming,
i'm studing the Echo example in ../omniORB-4.0.0/src/examples/boa
and my attenction is all about eg2_impl.cc file: in line 17 the class Echo_i is virtually derived from _sk_Echo. I was looking for definition of this class but i hadn't found it, it isn't in "becho.hh" where i was expect to found.

where is it?
Thanks,

Muzero

p.s. i beg your pardon for my terrible english!