The invention relates to a wellbore-lining tubing comprising at least one window pre-formed in the wall of the tubing and a device for selectively generating a fluid pressure pulse, and to a method of forming a lateral wellbore employing such a tubing.In an embodiment, a wellbore-lining tubing (130m) is disclosed which comprises: a tubing wall (32m), an internal fluid flow passage (30m), and at least one window (154m) pre-formed in the wall of the tubing; a device (34m) for selectively generating a fluid pressure pulse, the device located at least partly in a space (36m) provided in the wall of the tubing; and a coupling (190) for receiving a deflection tool (192) so that the deflection tool can be secured to the tubing and employed to divert a downhole component (202) through the window in the tubing wall.