In the thin-walled pre-meiotic asci of Chaenotheca chrysocephala a peripheral ascospore delimiting membrane cylinder was formed by transformation of membrane material generated by the proliferating plasma membrane. The ascus wall broke in parts and was degraded soon after the onset of secondary ascospore wall formation. Numerous lysosomes were observed prior to ascus deliquescence. The ascospores grew and their secondary wall layer became melanized after their release into the mazaedium.