MEDIAN EYES 719 



classical syndrome of macrogenitosoma preecox has been reported as occur- 

 ring in about 50% of cases in patients without pineal disturbances, while the 

 majority of cases of pineal tumours do not exhibit sexual syndromes 

 (Haldeman, 1927). It may even be that when these symptoms occur they 

 may be caused by pressure on neighbouring structures such as the pituitary 

 body and hypothalamus. The whole question of the existence of an 

 endocrine secretion and what it may do is thus unsolved. 



It is interesting that the association of the integumentary pigment with the 

 visual system is maintained in some amphibians ; thvis pigmentary changes always 

 occvir in 10-day-okl tadpoles if they are fed on pineal tissue (MeCord and Allen, 1917), 

 while the injection of pineal extract induces contraction of the melanophores of the 

 African toad, Xenopus (Bors and Ralston, 1951). 



The function of the parietal organ remained enigmatic until its eye -like 

 structure in lizards was described by Leydig (1872) and confirmed in Ayiguis 

 fragilis by De Graaf (1886) and in Sphenodon by Baldwin Spencer (1886). 

 From these observations arose the view that the pineal apparatus is a 

 primitive, unpaired, median, upward-looking eye, which has degenerated 

 except in a few instances. It is more probable, however, that the hypothesis 

 of Todaro (1888) is the more correct, that although often apparently un- 

 paired, the organ is the result of the fusion of a pair (see Sterzi, 1912 ; 

 Gladstone and Wakeley, 1940). The evidence derived from fossil remains of 

 extinct Vertebrates, the duplication of the organ in primitive tyj^es, its 

 occasional bifurcation in the higher species, and the frequent bilaterality of 

 its nervous connections, is convincing. There is a strong case to be made 

 that its primary function was sensory. In extinct fossil species it seems 

 clear that a median eye coexisted with lateral eyes, olfactory organs and 

 static organs, and the closure of the foramen in the roof of the cranium even 

 in these early t^^es indicates a regression of the organ and the loss of its 

 visual function even in remote geological times, a tendency possibly due to 

 the gradual predominance of the lateral eyes. Whether, as Patten (1890- 

 1912) suggested, the pineal organ is linearly derived from the median eye of 

 arthropods, particularly primitive arachnids, is a more debatable question. 



On the other hand, the view has been put forward that its optical 

 function is not essentially primitive but is rather the result of a secondary 

 transformation, in which case the pineal body of Mannnals cannot be looked 

 upon as a vestigial and metamorphosed remnant of an eye. According to 

 Tilney and Warren (1919) the histology of this region provides evidence that 

 in all Vertebrates this portion of the brain possesses a pluripotential activity. 

 Usually the fundamental tendency is in the direction of glandular formation, 

 the secretion being contributed in a few cases to the cerebro -spinal fluid, 

 but in most cases and in the Mammalia, to the blood stream as a hormone. 

 In some species (Cyclostomes, Amphibians, and primitive Reptiles) the arch 

 has become specialized with a visual function, an adaptive modification 



