MALE REPRODUCTIVE-BIOLOGY OF THE RED FROG CRAB, RANINA-RANINA, OFF HACHIJOJIMA, IZU ISLANDS, JAPAN

Male red frog crabs, Ranina ranina, were collected year round in 1990 and 1991 off Hachijojima for histological study of the reproductive sy stem and cycle. The testis containing the lobules and seminiferous duc ts is surrounded by connective tissue. The seminiferous duct connects to the anterior end of the vas deferens, which can be histologically d ivided into three portions similar to one another in appearance. It wa s surrounded by fibrous connective tissue, muscle fibrils and columnar epithelium. Muscle fibrils were absent in the anterior portion. Multi ple sperm masses were not formed in the vas deferens and ejaculatory d uct, but the sperm mass was covered with a capsule composed of two lay ers. The outer layer of the capsule was periodic acid Schiff (PAS)-pos itive, but the inner layer was negative. Both layers were Alcian Blue negative, except the vacuoles in the outer layer that were stained blu e. The small round androgenic gland was attached to the posterior end of the vas deferens of the coxa of the eighth thoracic appendage. The ejaculatory duct was distinguishable from the vas deferens by the abse nce of columnar epithelium and the presence of thick longitudinal musc le fibers. Spermatogenesis was histochemically examined. The acrosomal vesicle appeared to be derived from PAS-positive vesicles in the cyto plasm of the spermatid at the early stage of spermiogenesis. The arms were positive to the Feulgen reaction and the subacrosomal region was negative to PAS. Seasonal changes in reproductive cycle were inconspic uous histologically and microscopically. Sperm were always present in the testis and vas deferens throughout the year and occupied 5.1 to 19 .6% of testis observed in cross sections. The minimum size of maturity is less than 39 mm carapace length, but the minimum size capable of s uccessful mating was estimated to be ca. 55 mm.