Vertical shooter

i just did the vertical shooter tutorial, and the thing is this…

my enemyes goes from roght to left… what can i do to make my enemies fall from sky?..

heres the code:


function initDragons() {
for (i; i<dragons; i++) {
attachMovie(“dragon”, “dragon”+i, i);
dragon = _root[“dragon”+i];
updateDragons(dragon);
dragon.onEnterFrame = function() {
if (this.hitTest(arrows)) {
score += 5;
trace(score);
arrowActive = false;
removeMovieClip(arrows);
updateDragons(this);
}
if (this._x>0) {
this._x -= this.velo;
} else {
updateDragons(this);
}
};
}
}
initDragons();
function updateDragons(which) {
which._x = random(100)+530;
which._y = random(80)+20;
which.velo = random(10)+2;
}
this.onEnterFrame = function() {
checkKeys();
updatePawel();
updateArrow();
};

any one please