Having studied the functioning left ovary and the atrophic right ovary of the chicken during its in ovo embryogeny, we decided to study its development in vitro. For that purpose the explants of left and right ovaries of 7 at 19 days of in ovo development were cultured in Eagle medium, supplemented by bovine fetal serum and lated processed for structural and ultrastructural studies. At every ages the left ovary showed a cortex and a medulla while the right ovary had no cortex. Epithelial cells were observed in the cortex, encircling ovocytes having typical Balbiani's bodies formed by mitochondria, Golgi aparatus and centriole. Some nuclei were in the meiotic prophase. The right ovary and the medulla of the left ovary failed to show the lacunar aspect characteristic in the ovo study. Conversely, cell cords were found, formed by epithelial cells and ovocytes which being very close to each other, gave the cord a compact aspect. Among the cords, groups of interstitial cells could be seen, which were more frequent in the cultures of older ova and in both ovaries. The left and the right ovaries, therefore, developed according to the genetic pattern. Notwithstanding, the left ovary medulla and the right ovary would be modulated by extragonadal factors which would be inactive when the gonads are not in their natural environment.