The androgenic glands of the Pacific crayfish, Pacifastacus leniusculus trowbridgii Stimpson, 1859, were studied experimentally and by light and electron microscopy. The androgenic glands proliferate in the spring of the year concurrently with an increase in mitotic activity in the testes. Degeneration of a major portion of the glands occurs in the fall, when spermatogenic activity in the testes is near completion. Cellular development appears to progress from small undifferentiated cells through stages of vacuolization and hypertrophy and terminates with degeneration or lysis. The fine structure of the vacuolated gland cells is indicative of increased metabolic activity and probable hormone secretion. However, experimental manipulation of the glands of P. leniusculus gave no evidence of their presumed endocrine function. A discussion of the similarities of the androgenic glands with other known arthropod endocrine glands is also included.