A. Look for comp.lang.c++.
A. Simple put, that is the definition of the copy constructor. If it didn't have a parameter of a same-class reference, then it would be another type of constructor. What makes the copy constructor special is that when a copy of an object is needed, the copy constructor is invoked to construct it. For example:
void Foo( MGString X ); // Pass by value, copy constructor called
void Foo( MGString& X ); // Pass by reference, copy constructor not called
In the first form, since it uses pass-by-value syntax (as in C), the a copy of the original parameter must be made and passed to the function. The copy constructor is invoked to create that copy.