An ascus is a specialized sac-like structure found in certain fungi, particularly in the group known as Ascomycetes. This structure is responsible for producing and containing spores, which are essential for the reproduction of these fungi. Each ascus typically contains eight spores, although the number can vary among different species. The formation of ascospores occurs during a sexual reproductive process called ascomycete reproduction. When conditions are favorable, the spores are released from the ascus, allowing them to disperse and germinate into new fungal organisms. This reproductive strategy is crucial for the survival and spread of ascomycete fungi in various environments.