THE CENTRAL ROLE OF THE GENITAL DUCT IN THE DEVELOPMENT AND REGENERATION OF THE GENITAL ORGANS IN THE SEA URCHIN

Formation and regeneration of the genital papilla in the sea urchin, Hemicentrotus pulcherrimus were studied to find out what factor(s) control expression of the secondary sexual characters in the papilla. Surgical removal of various regions of the genital organ and the blood vessels was performed separately or in various combinations. The proximal part of the genital duct or its rudiment (D2 region) plays an essential role in the formation or regeneration of the papilla, and in the establishment of its sexual characters as well, i.e., if the D2 region is removed, papilla formation or regeneration is completely suppressed; when the D2 region is left uninjured, the papilla develops and displays the sexual characters even in the absence of the gonad, the distal part of the duct, a blood supply to the D2 region or all three of them combined. It can be concluded that the proximal part of the genital duct carries the factor(s) for determination and expression of the secondary sexual characters in the genital papilla. Discussion has been made about what factor(s) can be considered to reside within the cells of the D2 region of the duct.