1. Various components were tested as nutrients in media for barnacle tissue cultures. Bovine embryo extract and yeastolate were favorable additions for both cell outgrowth and organ cultures. Glucose did not improve the media. Bovine serum and Callinectes hemolymph had a negative effect. Mixed sera in concentrations higher than 10% were negative for both types of cultures. Addition of Minimum Medium Eagle and Medium 199 did not improve the barnacle culture media.2. In organ cultures mantle parenchyma were obtained for 25 days, ovarioles and cement glands for at least 7 days with no change in structure and organization. Mature oocytes and young immature oocytes were maintained for at least 7 days, and oogonia kept a high mitotic activity. Immature oocytes in later stages of development were not maintained.3. Extensive cell outgrowth forming large surface spreads and with cells showing high mitotic activity were obtained from attached explants for 18 days. The initial cell migration consisted of epithelial-...