Pond snail is widely distributed in rice field and pond in Japan except for Hokkaido. It is possible in the mature individuals of the pond snail to easily distinguish male and female only by observing the form of the right antenna. Because the right antenna of male bends like a hook and functions as a penis, while that of female is straight. In the childish male shell, however, the bending of the right antenna is not observed. Therefore, the bending of the right antenna in the mature male seems to be the secondary sexual character which is generated with the the testicular development.
In present study, molphological and histological changes in right antenna and testis in the male adult shell of Cipangopaludina japonica were examined in order to clarify whether the bending of the right antenna in male pond snail is secondary sexual character. As the result, the right antenna in male bends like a hook after the active spermatogenesis would be observed in the seminiferous tubule which was rapidly developed by the proliferation of reproductive cells. In addition, the histological changes with testicular development were observed in seminal duct which longitudinally passes through the inside of antenna and in the surface of antenna.
These results indicate that morphological and histological changes in the right antenna of the male adult shell of pond snail is the secondary sexual character which is generated with the development of seminiferous tubule.