A carcinoid occurring in the testis.

Carcinoids of the testis are rare tumours developing in three different ways: 1. It may differentiate within a teratoma, 2. it may be a metastasis of a "loco alieno" seated carcubiud abd 3. it may represent a real primary carcinoid. The observation of a primary testicular carcinoid in a man aged 55 years afforded the opportunity to study such a tumor for the first time by electron microscopic and fluorescence microscopic methods. Thereby, it could bw shown, that this testicular carcinoid corresponds to the carcinoids of the lower small gut. According to the specific ultrastructure of the intracytoplasmic granules it must derive histogenetically from an EC-cell. At the moment it cannot be decided whether the primary testicular carcinoid represents an autochthonous tumor of the male gonad or solely a teratoma with one-sided differentiation in the sense of a simplified teratoma.