1886.] 



On the Median Eye in Lizards. 



565 



The lens is cellular, and has a slight development of pigment in some 

 of its cells in the optic axis. 



Special connective tissue fibres pass, as in some other forms, from 

 the capsule to the edge of the lens. 



(e.) Leiodera nitida. — This may be taken as the type of several 

 forms, such as Calotes ophiomaca and versicola and Seps chalcidica, 

 in which the eye is lengthened out in a direction at right angles to the 

 optic axis. The lens is distinctly cellular, and continuous with the 

 hinder walls of the vesicle. The retinal elements consist of (1) rods ; 

 (2) a layer of round nucleated cells ; (3) a well marked clear space, 

 corresponding in position to the molecular layer ; and (4) an external 

 layer of cone-shaped elements. 



In these forms a nerve cannot be detected with certainty, though 

 very possibly with freshly killed specimens lis presence might be 

 demonstrated. 



In Leiodera the scale above the eye is beautifully modified, and a 

 transparent dome-shaped cornea developed, sections showing that the 

 pigment is absent from the scale in this region, though very abun- 

 dantly developed elsewhere. 



(/.) Varanus Bengodensis and giganteus. — The eye in these forms 

 will be dealt with fully on a subsequent occasion ; at present one point 

 only will be mentioned. In two specimens examined (perhaps of dif- 

 ferent species of Yaranus) the connexion with the proximal part of 

 the epiphysis was of an importantly different nature ; in one it was 

 in the form of a hollow process, in the other of a solid stalk, much 

 as in Hatteria. 



There can be no doubt that the connecting parts in the two instances 

 are equivalent to each other. 



(g.) Gyclodus gigas (?). — This may be taken as the type of those 

 forms, in which no structure comparable to an eye is at present found. 

 The distal extremity of the epiphysis is swollen out, the cells of its 

 Avails, which are thrown into folds, become shaped like those of cylin- 

 drical epithelium, and amongst them pigment is deposited, but no 

 true retina is formed, or any structure comparable to a lens. 



The distal swollen part of the epiphysis is enveloped in pigment in 

 the dura mater, some distance in front of the proximal part, with 

 which it is connected by a hollow process. The whole structure lies 

 on the inner side of the cranium, closely fitted to the bone, as in 

 Lacerta, ocellata. 



The scale on the surface of the head is imperfectly modified to form 

 a cornea, and has the appearance of degenerating. 



