274 THE PINEAL ORGAN 



cases indicated by a modified scale and a transparent parietal spot. 

 According to Studnicka's observations on one specimen of Draco, there is 

 no parietal eye, but the pineal organ ends in a dorso-ventrally compressed 

 end vesicle which lay beneath a parietal pit closed superficially by a lamella 

 of cartilage. The end vesicle was not pigmented. 



Calotes ophiomachus. 



In a specimen described by Spencer (1886) there was a pentagonal 

 corneal scale (Fig. 192, B) with the broad end anterior ; a little behind the 

 centre of this was the parietal spot which was slightly convex superficially 





A B C 



Fig. 192. — The Parietal or Corneal Scale and its Surroundings in Three 



Forms of Reptiles. 



A : Varanus giganteus (after Spencer) ; B : Calotes versicolor, a tree lizard so 

 named on account of its power or changing its colour (after Spencer) ; C : 

 Lacerta muralis, var. cozrulea (after Leydig). In the centre of the parietal plate 

 is seen the parietal eye spot ; through this is seen in Calotes, in which this 

 part is definitely transparent, the parietal eye. In Lacerta muralis pigment 

 granules encroach on this area. 



and bounded by a circular rim. The parietal eye was a dorso-ventrally 

 flattened vesicle having its longest axis in the median plane. Some of 

 the cells of the lens contained pigment at their inner or central ends. 

 The parietal organ was separated from the epiphysis. The latter consisted 

 of two parts, a vertical basal segment and a horizontal terminal part which 

 was directed forward, its tip ending at the posterior border of the parietal 

 foramen near the parietal eye. 



Agama hispida. Spencer (1886). 



The parietal eye lay in a parietal foramen, beneath a pigmentless 

 parietal cornea and modified scale, through which could be seen a 

 remarkable hour-glass-shaped parietal spot. The retina of the parietal 

 eye was so deeply pigmented that its structure was obscured, and pigment 

 was also present in the lens. 



