Morphological and ultrastructural features of LM38-LP and LM38-HP subcutaneous tumors. Light microscopy of Maraglass-embedded sections confirmed that LM38-LP (a) heterogenous tumor parenchyma was composed of two main cell types: small epithelial cells (e) of light cytoplasm and euchromatic nuclei with distinct nucleoli and some dense chromatin granules found close to the lumen, and basal myoepithelial (m) dark cells with intensely stained irregular nuclei and large nucleoli, placed near the stroma (s) or mixed at random with the small light cells. The LM38-HP tumors (b) were mainly made up of small light epithelial cells. (Original magnification ×400; scale bar,35 μm.) Electron micrographs of LM38-LP tumor showing the two subpopulations at low magnification (c) (original magnification ×8000), a detail of the characteristic nuclei, nucleoli and cytoplasm of the light epithelial cells (d) (original magnification ×14,000) and the presence of abundant parallel microfilament bundles (arrow) and focal densities (arrowhead) in a cytoplasmic process of a dark myoepithelial cell (e) (original magnification ×17,000). Glandular lumina with microvilli and rudimentary intercellular junctions in LM38-HP tumor (f) (original magnification ×40,000), confirming its glandular epithelial origin.