Thomas tissue embedding cassettes, with separate plastic lids, eliminate problems often associated with integral hinged lids. Hinge breakage during shipping and unnecessary sample contact or loss while detaching integral lids can be time consuming and expensive. Thomas cassette lids incorporate a deep, plug seal design to position and lock lids securely on the cassette. This design allows for reopening cassette to reposition sample without premature lid separation. Dense polymer material will not float, resists heat, solvents, decalcifying solutions, and is compatible with microwave techniques. Vertical flow-through slots maximize fluid exchange while eliminating residual tissue and caustic solvent entrapment. Rigid, reinforced rib construction in cassette base eliminates "chatter" during sectioning. Textured writing surface on three sides offers more labeling area. Cassettes are ideal for use with shur-mark labeling instrument and other auto-labeling equipment. Offered in natural and eleven pastel colors for easy separation and identification of specimens. Cassettes accept reusable metal lids, fit stainless steel and disposable plastic base molds, microtome chucks, chuck adapters, and other storage systems. Cassettes are fully compatible with ames tissue-tek fisher histoprep, AO histostat, and other processing/embedding equipment.