The structure and function of the male accessory reproductive gland system of the cotton stainer, Dysdercus fasciatus Signoret, was studied using ultrastructural techniques. The gland system is composed of a pair of mesadenia and an ejaculatory duct, whose anterior end is swollen and encloses a glandular structure whose origin is not clear. Each mesadene is composed of a large number of sacs whose lumina are confluent. The epithelium of each sac is one cell layer thick and is composed of two cell types, mononucleate and multinucleate cells. The origin and siginficance of the multinucleate condition in the mesadenial epithelial cells is not clear, but it is suggested that this condition might have arisen during maturation, when mitotic divisions are complete, but the nuclei continued to multiply within an increased cytoplasmic mass, which itself does not divide.
