In an embodiment of the invention there is provided a membrane fitment designed and sized to be inserted into the orifice defined by a container. Retention structure on the fitment cooperates with complimentary structure on the internal wall of the container orifice to secure the fitment within the orifice such that the combination forms an excellent primary seal. Tamper evidence is offered by the normal requirement for initial membrane removal. Novel designs for the membrane, its associated pull ring, and the frangible removal structure are taught in various embodiments. The novel designs may promote facile initial removal suitable for a child. In addition, the novel designs avoid the potential hazards presented by prior art membranes.