The testes of Lepidoptera are usually ovoid, paired organs suspended in the abdominal cavity. The sheath surrounding each testis has two prominent cellular layers. The outer cells cover the circumference of the testis, while the inner layer also extends into the lumen to form the walls of the four follicles. Germ cells develop as clones within each follicle lumen. 1 Shortly before pupation, the testes of many species of Lepidoptera fuse and twist to form a single organ. This process requires ecdysteroid. 2 Male tract development is also dependent on the presence of ecdysteroid. 3 Release of sperm from the testis to the male genital tract in adult male Lepidoptera is negatively controlled by ecdysteroid. 4