282 THE PINEAL ORGAN 



had become greatly enlarged. This consisted of a proximal vertical 

 segment and a horizontal part which was directed forward ; it showed 

 saccular outgrowths and ended in a pointed extremity, the walls of which 

 were of equal thickness. 



The parietal eye, which is only present in the embryonic stage of 

 development, has a distinctly biconvex lens consisting of elongated cells 

 and a retina containing brown pigment. The retinal cells ended in long 

 rod-like processes, which projected into the lumen of the vesicle ; and 

 between the bases of these small round cells could be distinguished. 

 Neither nerve-fibres nor parietal nerve could be recognized. No parietal 

 foramen was present, nor was there any specially modified corneal scale, 

 the scales in the pineal and the surrounding region being small and of 

 approximately equal size. 



The published description of other species of the Skink family, 

 such as Scincus officinalis, Hinulia, and Chalcides tridactylus, do not 

 differ essentially from that of Cyclodus and Gongylus, and it will be 

 unnecessary to give a special account of each of these. It will suffice 

 to give a general idea of the structure of the pineal organ by the drawing 

 (Fig. 194) reproduced, with the kind permission of the author, from 

 a photograph of a section through the parietal eye of Scincus officinalis 

 and published by Jean Calvet in his work L'Epiphyse, 1934. This shows 

 the lens, retina, and parietal nerve, with the general relations of the 

 organ. Calvet also gives photographs showing the position of the parietal 

 scale in Varanus and Iguana. 



Rhipidoglossa. 



This family, which is represented by the chamaeleons, is from the 

 standpoint of the pineal system as remarkable as it is in other respects. 

 The pineal system in general resembles that of Lacerta, but although 

 all parts of the complete system are represented in the embryonic con- 

 dition, the parietal organ in some examples has disappeared in the adult 

 animal. A detailed account of the pineal system of chamaeleons was given 

 by Spencer in 1886 and one two years later by Owsjannikow. In both of 

 these examples and in another mentioned by Studnicka, which was 

 examined by himself, there is substantial agreement with reference to the 

 presence of a parietal foramen. In Studnicka's case the contained parietal 

 organ was surrounded on all sides by a dense plexus of anastomosing 

 vessels, and in all, the tissue overlying the organ was devoid of pigment and 

 its position on the head was indicated by a small, slightly raised transparent 

 scale or nodule. According to Spencer's description, the pineal organ 

 (epiphysis) was a hollow, tubular structure, which was directed at first 

 dorsally and was then bent sharply forward. In its distal part the 



