196 W. BALDWIN SPBNOER. 



which is devoid of pigment, and transparent enough to allow of 

 the eye beneath being seen as a dark spot. In larger speci- 

 mens (fig. 15) the central part is still more raised, and forms a 

 dome-shaped structure. In the figure, which is twice the size 

 of the original, the scales from the dorsal surface of the head 

 are represented, and the prominence of the scale with its 

 modification to form a cornea can be seen. The only wonder 

 again is that long before this a careful examination of the 

 structure has not been made. 



Structure. — The eye lies within the parietal foramen, which 

 is well developed in Iguana, surrounded closely by connective 

 tissue, there being no capsule present. The eye is so placed 

 that its optic axis is as nearly as possible in the vertical line. 

 In shape it simply resembles an inverted cup with the lens, 

 which has a flattened external surface, occupying the anterior 

 end. The organ is usually more cup-shaped and symmetrical 

 than the one figured (PI. XVII, fig. 23) ; but this, which is 

 drawn without any of its surroundings, will serve to demon- 

 strate the structure as far as it will be described in the present 

 communication. 



Lens, — The lens is convex posteriorly, and almost — due to 

 its anterior surface being flattened — plano-convex in shape ; it 

 is distinctly cellular, with well-marked nuclei scattered irregu- 

 larly in section. On either side it thins out to join the walls of 

 the posterior part, in which, at the line of union, a specially 

 deep circular ring of pigment is deposited. 



Retina. — The rods (R) are well marked and embedded in 

 deep pigment. In the line of the optic axis is a bundle of 

 specially elongated ones (E}) ; externally they are in contact 

 with spherical elements («^), which are as usual of, roughly 

 speaking, the same size as the nuclei of the lens cells. These 

 elements, together with the external ends of the rods, appear 

 to be surrounded by a molecular layer of punctated material, 

 clearly distinguishable, but yet not so well marked as in 

 Varanus giganteus. Most externally is a layer of cone- 

 shaped bodies {Co.'), the internal ends of which taper off into 

 processes connecting them either with the spherical elements 



