title: An enigmatic eye: the histology of the tuatara pineal complex.
abstract: OBJECTIVE
  To examine the histology of the tuatara pineal complex and to compare findings with those of Dendy. Some reptiles have an anatomically sophisticated pineal complex with a median pineal eye, a paraphysis and a pineal sac. In comparison, the human pineal gland is simple and homogenous and thought to be a phylogenetic relic. It is now considered a neuroendocrine gland the function of which is still not fully understood. Its simple anatomical structure is in contrast to its biochemical complexity; its secretions (the most studied being melatonin) modifying the function of the adeno- and neurohypophysis, thyroid and parathyroids, adrenal cortex and medulla, endocrine pancreas and the gonads.
  
  
  METHODS
  Histological sections of the brain of a neonatal tuatara were studied by light microscopy.
  
  
  RESULTS
  The histological findings of the pineal eye demonstrated a cornea-like structure, rudimentary lens and simple retina. The adjacent paraphysis was a large, multisaccular organ and the pineal sac a very large saccular organ with a poorly differentiated retina.
  
  
  CONCLUSIONS
  The pineal eye of the tuatara has a remarkably eye-like structure with photoreceptors that in other reptiles have been shown to exhibit photoreceptive capabilities. The paraphysis appeared to have a secretory function that is as yet undetermined, while the pineal sac had the appearance of a poorly differentiated retina. Thus it appears that the complex biochemistry of the human pineal gland is reflected in the complex anatomical structure of this primitive reptile.
authors.affiliation: Department of Ophthalmology, Dunedin Hospital, New Zealand.
authors.forename: Casey Y-J
authors.initials: CY
authors.lastname: Ung
authors.forename: Anthony C B
authors.initials: AC
authors.lastname: Molteno
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D005075:Biological Evolution; D009799:Ocular Physiological Phenomena; D020419:Photoreceptor Cells, Vertebrate / Q000166:cytology / Q000502:physiology; D010802:Phylogeny; D010870:Pineal Gland / Q000033:anatomy & histology* / Q000502:physiology; D012104:Reptiles / Q000033:anatomy & histology* / Q000502:physiology