A histology processing cassette stack having a plurality of cassettes for use in analyzing or processing biological samples is disclosed. The stack of cassettes are arranged in register and threaded on a connecting strip which passes through an aperture in a direction perpendicular to the plane of the cassette though a front wall of the cassette. The cassettes are held in fixed relation and may be transported and inserted en bloc into a magazine in a printing system by the connecting strip having a retaining part abutting the bottom cassette and able to bear the weight of the stack of cassettes when suspended. A printing system comprising a housing having a void for receiving a magazine loaded with the stack of cassettes is also disclosed.