PARIETAL FORAMEN OF REPTILES 27I 



Iguana (Klinckostroem, 1894). In one instance in Sphenodon (Spencer) 

 the central axis of the parietal organ was directed obliquely forward, 

 so that rays of light entering through the foramen could only fall directly 

 on one part of the retina. This condition is, however, exceptional and 

 does not appear to have been described in other adult specimens. Dendy's 

 figures show a less pronounced degree of obliquity in two embryos of 

 Sphenodon, but it is probable that this condition would have been rectified 

 by the time the animal had reached maturity. 



More important from the standpoint of interference with function 

 is the occurrence of pigment in the substance of the lens — Anolis (Spencer), 

 Anguis fragilis (Beraneck), Varanus (Spencer) ; and the encroachment from 

 the surrounding tissue of black pigment, which may grow inward over the 

 area occupied by the subjacent lens, as in a case described by Leydig of 

 Lacerta muralis (1891) ; also, irregularity in form and structural degenera- 

 tive changes, previously alluded to as occurring in the lens of a specimen 

 of an adult Iguana described by Klinckowstroem (1894). Calcareous 

 concretions have also been found in the parietal foramen, which, although 

 in relation with the end vesicle of the pineal organ rather than the parietal 

 organ, indicate localized degenerative processes occurring within the area 

 of the pineal system. These concretions have been noted by Leydig 

 (1891), who described four rounded, calcareous nodules lying over the 

 tip of the epiphysis, and by Studnicka, in Varanus nebulosus, who found 

 similar structures in the neighbourhood of the pineal bud. In this case 

 there was one large and several small calcareous balls, the latter being 

 arranged in a semicircle around the pineal outgrowth. These conditions 

 indicate not only interference with function and degenerative changes in 

 the living animals in which they have been observed, but loss of function 

 of the parietal eyes and accompanying degeneration of structure, which 

 must have commenced in quite remote ancestors of the living generations 

 of reptiles. The parietal cornea, corneal scale, and parietal spot of reptiles 

 have already been alluded to in the general description of these structures. 



Notes on the Pineal System of Special Examples of 

 Living Saurian Reptiles 



Further reference to the significance of the parietal foramen of extinct 

 Saurian reptiles will be made in the chapter on the morphology of the 

 skull in so far as it is concerned in the geological evidence of the antiquity 

 of the median and lateral eyes of vertebrates. The following notes will 

 deal chiefly with the pineal system of embryonic and mature examples of 

 different types of lizard. 



