A study of chick embryo and horse placental tissue cultivated in tissue culture with the yeast phase of H. capsulatum by the cover-glass method, showed that fibro-blasts or fibroblast-like cells of the outgrowth contained a greatly increased number of organisms in the cytoplasm. A unique form of Histoplasma was seen for the first time consisting of numerous globose sacs containing myriads of encapsulated yeast cells surrounded by a well-defined membrane. These sacs, 20-300u in diam., bore a striking resemblance to the in vivo form of Coccidioides immitis.