In a high magnification light micrograph, the interstitial cells of the testis have a foamy appearance. The "bubbles" in the cytoplasm are the light microscopic appearance of lipid droplets from which the steroid hormones are made. The darkly stained organelles are nuclei (n). The open spaces are small blood vessels (bv) that are lined by endothelial cells. The cells within the seminiferous tubules that have a mottled appearance are primary spermatocytes.