DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Giant roundworm. Light micrograph of a transverse section through a male giant roundworm (Ascaris lumbricoides). The body is covered in a thick cuticle (brown), which is secreted by the underlying hypodermis (black). Below this are layers of muscle (pink). The gut is at centre. It is surrounded by several circular testes undergoing spermatogenesis (sperm production). Magnification: x4 when printed at 10 centimetres wide.
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