276 THE PINEAL ORGAN 



organ. The latter is generally regarded as the fibrous sheath of the nerve 

 of the parietal organ, the fibres of which have disappeared. It must 

 be remembered, however, that in Lacerta vivipara and other species the 

 parietal nerve has been shown by NowikofT to be developed independently 

 and in front of the epiphyseal evagination, after the parietal organ has been 

 separated from the epiphyseal part of the primary diverticulum. 



Anolis. 



One specimen described by Spencer (1886) differs from the typical 

 in that the long axis of the parietal organ is vertical, and that it lies in an 

 exceptionally narrow parietal foramen which is almost completely filled 

 by the parietal eye. It was connected with the epiphysis by a fibrous 

 cord, which was regarded by Spencer as its nerve ; but, as pointed 

 out by Studnicka, the cord as shown in Spencer's figure is clearly con- 

 tinuous with the fibrous sheath of the parietal organ, and no fibres are 

 seen entering the retina. In another specimen of Anolis described by 

 Spencer, the parietal organ was dorso-ventrally flattened. It is probable, 

 therefore, that the cylindrical parietal organ of the first specimen was 

 exceptional, and does not represent a peculiarity of this particular family. 

 The central cells of the lens in its deepest part contained pigment in the 

 first specimen. 



Leiolcemus nitidus (Spencer, 1886). 



The parietal organ (Fig. 193) is dorso-ventrally flattened ; the central 

 part of the retina is slightly arched upwards towards the lens, so that the 



Fig. 193. — Sagittal Section through the Parietal Eye of Leiolcemus nitidus, 

 showing a Flattened, Undifferentiated Retina of Ependymal Type, 

 Biconvex Lens, and a Corium with Exceptionally Tall Papilla. (After 

 Spencer, 1886.) 



lens : lens. 



cor. : conum. 

 cut. : cuticle. 

 ep. : epidermis. 



ret. 



retina. 



cavity of the organ is much reduced in its vertical diameter ; the lateral 

 walls formed by the peripheral part of the retina are almost vertical, but 



