Leydig's organ (named after the German histologist

Franz Leydig Franz von Leydig, also Franz Leydig (; 21 May 1821 – 13 April 1908), was a German zoologist and comparative anatomist."Franz von Leydig" (biography), Ole Daniel Enerson, 2006, WhoNamedIt.coWNI-675-Leydig Life Franz Leydig was born on 21 May ...

who first described it in 1857) is a unique structure found only in some, but not all,

elasmobranchs Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having five to seven pairs of gil ...

(

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...

s and

rays Ray may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), a bony or horny spine on a fin Science and mathematics * Ray (geometry), half of a line proceeding from an initial point * Ray (gra ...

). Nestled along the top and bottom of the

esophagus The esophagus ( American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to ...

, it produces

red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

s, as do the

spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .

and special tissue around the gonads. Heterophilic and

eosinophilic Eosinophilic (Greek suffix -phil-, meaning ''loves eosin'') is the staining of tissues, cells, or organelles after they have been washed with eosin, a dye. Eosin is an acidic dye for staining cell cytoplasm, collagen, and muscle fibers. ''E ...

granulocytes are produced, closely resembling structures of mammalian plasma cells. Leydig's organ is part of the immune system.Mattisson, A., & Faänge, R. (1982). The Cellular Structure Of The Leydig Organ In The Shark, ''Etmopterus spinax'' (L.). The Biological Bulletin, 162(2), 182–194. doi:10.2307/1540813

Notes

References

* Fish anatomy {{shark-stub