Why the flash creates extra instaces of the class

I have linked a MovieClip to a class. After that I have places some movie clips of them on the stage. And now I like to do something with them, but I couldn’t because some extra instances are created (I wonder how???) and they make me problems.
The names of instances of the class I placed on the Stage are legs1 legs2 legs3, …
and the extra instances are: instance21, instance25,…(and they are not visible on the Scene)
I really want to remove them!Could anyone help me , please?