CHAPTER 20 



REPTILES 



It is in the class Reptilia that the greatest insight into the nature of 

 the pineal system has been obtained, and more especially with reference 

 to the pineal eye of that archaic lizard, the Tuatara of New Zealand, or 

 Sphenodon, which has sometimes been alluded to as a " living fossil." 



Most valuable information has also been gained by the study of the 

 parietal foramen in the various orders of fossil reptiles, which, like that 

 in Pisces and Amphibia, not only indicates the antiquity and universality 

 of distribution of the median eye in the widely separated orders of the 

 class, but that, judging from the large size of the foramen in some of the 

 more primitive examples as compared with their living representatives, 

 the pineal eye itself is, both actually and relatively to the size of the animal, 

 smaller in living species than it was in their remote ancestors. 



As in fishes and amphibians, there is indubitable evidence of two 

 organs being included in the pineal system of reptiles ; there is a difference 

 of opinion, however, as to whether the two components are essentially 

 separate and independent median structures or whether they are derived 

 from a primarily bilateral pair of sense organs which are homologous 

 with each other and have been secondarily shifted into the median plane. 



There is in reptiles the same subdivision of the whole pineal organ 

 into proximal part, stalk, and end vesicle, as in fishes and amphibians, 

 and there are the same connections with the roof of the diencephalon. 

 There is, however, much variability in the degree of differentiation of the 

 pineal system in different orders of the class and in individual species. 



Valuable information has also been gleaned from the study of accessory 

 parietal organs in reptiles and of the degenerative changes which have 

 been observed in some cases, e.g. the presence of pigment in the lens ; 

 absence or inconspicuous appearance of the parietal spot ; and degenerative 

 or pathological changes in the neuro-epithelial tissue. 



In Crocodilia neither parietal organ nor epiphysis is present in the 



adult animal, although the habenular and posterior commissures are 



well-developed and distinct, being separated by a small part of the roof 



of the diencephalon ; the dorsal sac and paraphysis are also present — 



alligator (Sorensen, 1894) 5 Crocodilus madagascarensis and Caiman niger 



(Voeltzkow, 1903). 



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