The development of ascocarp and the nuclear behaviour during the development of ascus and ascospores was studied inAchaetomiella megaspora(Sörgel) D. Hawksw. The ascocarp initials arise by the coiling of a hyphal branch, the ascogonial coil. The septate, multinucleate ascogonial coil soon becomes invested, forming a spherical ball of pseudoparenchymatous mass, which later on differentiates into a central sporogenous core and wall layers. The asci were developed from typical croziers, produced by the binucleate ascogenous cells. Young ascus undergoes meiosis forming 2 and 4 nucleate stages, followed by a mitotic division which results into an eight nucleate ascus. Cell wall is laid down around each nucleus to form the young ascospores. The ascospores generally have a single nucleus, but sometimes become binucleate due to mitotic division of their nuclei. The haploid chromosome number for this species is 5(n=5).