ABSTRACTEven though spores ofAscobolus immersusare much larger than those of any other species of the genus, ascosporogenesis in this species is basically identical to that of other species ofAscobolus.The spinelike precursors of the epispore layer are connected laterally into numerous periclinal lines. A dark band is formed above the layers of epispore and leaves a translucent zone separating the epispore from the matrix of the perisporic sac. The appearance of a translucent zone causes a fragile“exospure”similar to that found consistently in many coprophilous and pyrophilic discomycetes. Globular opaque bodies of epiplasmic origin and surrounded by amorphous electron dense granules are found in the perisporic sac and appear to be involved in ornament formation. Perisporic sac vacuoles that influence spore ornamentation inA. immersusare contrasted with those of other species ofAscobolus.