Apparatus for forming an underground passageway and simultaneously laying therein a conduit or other elongate components comprises a rotary drill member coupled to a rotary and axially movable drill stem. The coupling is one which virtually automatically enables the drill stem to be coupled to and uncoupled from the drill member and comprises as one embodiment interlocking driving lugs carried by the drill stem and the drill member. The driving lugs are sandwiched between telescoped portions of the drill member and the drill stem and thereby are reinforced by such portions of the drill stem and the drill member in such manner as to preclude movement of the driving lugs in both radially inward and radially outward directions. Other couplings can be used.