A variety of cell types develop when cells of 6 1/2-8 1/2 h Drosophila embryos are cultured in an improved medium. Nerve, muscles, fat-body, chitin-secreting, and macrophage-like cells (possibly haemocytes) appear in the first 24 h and mature over the next week. Tracheal, imaginal disc, a second stage of the macrophage-like, and a anumber of unidentified fibroblastic and epithelial cells appear in the 2nd and 3rd week, following a resumption of cell multiplication. There is some organization of some of the cell types into higher structures.