ACE C++ Library class ACE_TASK doesn't have any activate function?

I have seen how to launch threads in my project, where we are using ACE library . But I have a question when ACE_TASK doesn't have any activate function how can you call it in class derived from MyClass class . The activate function is in ACE_TASK_BASE class which is derived from ACE_TASK . But MyClass class and ACE_TASK_BASE doesn't have any direct relation ?

class MyClass: public ACE_Task< ACE_MT_SYNCH >   {
    public:
    //derived from ACE_Task
    virtual int open( void *arg = NULL );
    //derived from ACE_Task
    virtual int svc();
};

//then we are calling

this->activate();    //  ?????

in open(); //running our job in

int svc() {
    while( _running )
       ....
}