STEVE LOWRY / SCIENCE PHOTO LIBRARY STEVE LOWRY / SCIENCE PHOTO LIBRARY
Polarised light micrograph of cross section of porcupine (Erethizon dorsatum) quill. These quills, like hair and horns, are made of keratin. The quills are not hollow, but have a honeycomb structure. Porcupines produce a pungent warning odour when their quills are erected. Quills also contain a fluorescent material that brightens the quills at night, when the porcupine is most likely to meet predators. Magnification: x40 at 10cm wide.
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