STUDIES ON THE BREEDING BIOLOGY OF THE EEL (ANGUILLA JAPONICA TEMMINCK SCHLEGEL)3. HISTOLOGICAL AND CYTOLOGICAL STUDIES ON THE GONADAL DEVELOPMENT OF EEL

The gonadal development of eel was studied histologically and cytologically. The development of testis is composed of six stages: 1) early multiplication of spermatogonia; 2) late multiplication of spermatogonia; 3) growth and maturation of spermatocytes; 4) initial appearance of spermatozoa; 5) complete maturation of spermatozoa; 6) degeneration of spermatozoa. The oogenesis is composed of ix phases: 1) oogonia; 2) oocyte with follicular epithelium consisting of a single layer of follicle cells; 3) oocyte with adipose vesicles; 4) oocyte filled with yolk; 5) oocyte with migratory nucleus; 6) degeneration of oocyte. Based on the six phases of oogenesis, the development of ovary is also composed of six stages correspondingly. The staging of gonadal development of eel, the mode of yolk formation, the spawning type and other questions were discussed.