#ductule__ductulus  a very small duct
  supertype:  #duct__canal__channel  a bodily passage or tube conveying a secretion or other substance
  subtype:  #sweat_duct__sweatduct  a small duct that conveys sweat from a sudoriferous gland to the surface of the skin
  subtype:  #biliary_ductule  excretory ducts of the liver; empty into the hepatic ducts

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