Histological observations of the gonad in Cyclina sinensis.

To gain a better understanding of the spawning mechanism and a better sampling of the gonad for estimating gonad development in Cyclina sinensis, a detailed study of the morphology and histology of its gonad was made. The gonad consists of a large number of acini connected with one another by gonoducts. Terminal gonoduct leading to the genital aperture formed the vesicle for an accumulation of sex products prior to spawning, and the genital aperture led to dorsal region of the inside mantle cavity of inner demibranch. The dorsal region of the gonad was occupied by the vesicle and the terminal gonoduct. So, it is considered that the samples obtained from a part of the abdominal half of gonad are better than those from the dorsal half to estimate gonad development and gonad index.