The membrane shell of an implantable dosage system according to the inventionis particularly suitable for subcutaneous applications to release an activeagent with steady amounts during a longer period of time. The membrane shell (3)according to the invention comprises a first half (1) and a second half (2), whichboth halves comprise a continuous closure edge (8, 9), and are adapted to be connectedto each other through a closable joint. The closure edges (8, 9) of the halves compriseat least one groove (10) and/or at least one protrusion (11) as continuous or discontinuous,and the membrane shell (3) is adapted to be closed so that at least one protrusion(11) and/or at least one groove (10) of the second half becomes opposed to at leastone groove (10) and/or at least one protrusion (11) of the first half through asnap-fit joint.
