Some endocrine glands of the carp-funa hybrid were studied with a light microscope to elucidate their detailed structure and the possible causal factor of sterility in the males. Adult specimens of carp (Cyprinus carpio), gengoroh-buna (Carassius auratus cuvieri), and their hybrid (F₁) were examined.
The hybrid males are sterile as manifested by the failure of meiosis and seminomatous neoplasm in their testes. The hybrid females revealed well-developed ovaries, but their fertility was not tested.
The hybrid hypophysis shows an intermediate condition between the parent species in the grade of ramification of the pars nervosa into the pars intermedia. Among seven types of granular cells demonstrated in the adenohypophysis, certain degenerative and anomalous changes are recognized only in the gonadotrophs of the hybrid hypophysis, especially in the female. These changes are discussed as a possible cause of sterility. A considerable amount of aldehyde fuchsin stainable neurosecretory material occurs in the cells of the nucleus preopticus and in the pars nervosa. The nucleus lateralis tuberis exhibits a histologically healthy condition.