DON W. FAWCETT / SCIENCE PHOTO LIBRARY DON W. FAWCETT / SCIENCE PHOTO LIBRARY
Colour enhanced transmission electron micrograph of lipid (red) in a Sertoli cell from opossum testes (Didelphis virginiana). The lipid that accumulates within cells for internal use is not limited by a membrane but takes the form of spherical oil droplets suspended in the aqueous cytoplasmic matrix. In the accompanying micrograph, the lipid was intensely blackened by osmium even though primary fixation was with glutaraldehyde. The droplets have maintained their normal spherical form.
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