186 W. BALDWIN SPENCER. 



/ 



Reference to this structure of the retina will be made again 



when dealing with the epiphysis in Cyclodus. 



(3) The triple nature of the pineal stalk. 



Varanus bengalensis, PL XV, fig. 12; PI. XVI, fig. 17; 

 PI. XIX, figs. 37 and 41. 



External Indication. — In the several specimens of Vara- 

 nus examined (in addition to V. giganteus) the external in- 

 dication of the eye was very clear indeed, consisting of a large, 

 modified, median scale (PI. XIX, fig. 37), lying somewhat 

 posterior to the level of the paired eyes, and having at its 

 centre a circular dark space, surrounded at a short distance by 

 a dark circular line. The central part, which is to a certain 

 extent transparent, acts as a cornea for the eye placed beneath. 



Position of the Eye. — In small specimens of Varanus, 

 when the skin is removed from the head, the pineal eye is 

 removed with it and may be examined whole. Fig. 12 repre- 

 sents a portion of the skull roof of a very young specimen of 

 V. bengalensis viewed from the under surface, the bone 

 being very thin indeed. The portion surrounding the parietal 

 foramen is represented in the figure, together with the pineal 

 eye, lying in the latter and viewed as a solid object. The 

 foramen has a somewhat oval shape and backwards from it 

 leads a groove in the median line. The specimen from which 

 this is taken was not in good histological preservation, and no 

 connection with the brain can be traced. The eye is circular 

 in outline and depressed from above downwards, and shows, 

 when viewed by transmitted light, the rods embedded in pig- 

 ment and forming a very definite layer. Since they line a 

 space within the vesicle, circular in outline, those at the sides, 

 when the object is viewed from above or below, form a circle (R), 

 external to which lie the other elements of the retina. In the 

 optic axis posteriorly lies a prominent mass of rods more deeply 

 pigmented than elsewhere, and which indicate most probably a 

 series of elongated rods connected with the union of the pineal 

 stalk ; the latter may have been pulled away along with the 



