Initialising cl***** with pointers to this

I don't understand the following line of code.  Please note that, as
my naming suggests, DerivedClass is a class that is derived from
BaseClass.

virtual BaseClass* clone() const{ return new DerivedClass(*this);

My confusion arises from the fact that DerivedClass appears only to
take the default constructor, initialised with ()

So how does DerivedClass(*this) make sense when all objects of
DerivedClass are constructed via a constructor with no parameters?

I know this is a basic question about a fairly common type of c++
construct, and I'm eager to learn more.

Thanks for your help,

Paul Epstein