200 W. BALDWIN SPENOER. 



thus the appearance, viewed from above, of a white rim sur- 

 rounding a dark circular space, and lying immediately beneath 

 the scale, is easily visible on the dorsal surface of the head. 



Calotes ophiomaca and C. versicola. — In both these 

 species the external indication is very clear, the modified scale 

 with its corneal, central part forming a prominent object on 

 the surface of the head : internally the structure is practically 

 the same in both forms, and the description which follows is 

 that of the first mentioned of the two species. 



Position of the Eye. — The organ is considerably smaller 

 than the foramen in which it lies, and is enclosed in connective 

 tissue ; the inner fibres of the cutis vera are so arranged as to 

 form a dome-shaped structure above the eye (Ct.^) whilst there is 

 the usual marked absence of pigment between the latter and 

 the external surface, which is also dome-shaped. The cells of 

 the rete mucosum are noticeably elongated and columnar im- 

 mediately above the eye [R.M.). 



Structure. — The whole organ is considerably compressed, 

 in the dorso-ventral line, its longest axis (PI. XVIII, fig. 33) 

 lying in the same line with that of the head. 



Lens. — The lens is distinctly cellular though the nuclei of 

 the component cells are not clearly visible (fig. 33, Le.) as in 

 other form such as Seps (fig. 32). The structure is concavo- 

 convex in shape, its anterior surface being convex outwards, 

 whilst certain of the ceils on the inner side have become pig- 

 mented {pig.) and thereby assumed a striking similarity to 

 the rods. 



Retina. — The rods (jR.) are very well developed, facing into 

 the cavity of the optic vesicle ; from their external ends pro- 

 minently marked processes pass to an outer layer of cone-shaped 

 bodies (Co.), the broad bases of which lie upon the external 

 limiting structure of the eye. There is an absence of any 

 spherical elements such as are seen in other forms. As before 

 said, no nuclei can be recognised in the lens, and the failure to 

 detect both may very probably be due to the fact that the 

 specimen was not in a very good state of histological preserva- 

 tion rather than to their being absent. 



