REPTILES 



367 



like a contact glass and separated from it by a closed conjunctival sac as is seen 

 in snakes (Schwarz-Karsten, 1933 ; Walls, 1934 ; Verrier, 1936 ; Rochon- 

 Duvigneavid, 1943). In such cases the spectacle may be surrounded by a rim 

 of tiny scales, as in Ablepharns, Ophiops, or the geckos (Fig. 435) ; alternatively, 

 as in snakes, such a rim-formation is lacking and the spectacle is inserted 

 into the ordinary arrangement of the scales of the head (Fig. 436). It is 



Figs. 435 to 441. — The Eyelids of Lizards. 



Fig. 43.5. — Ablepharus. 



Fig. ■iZQ.— TyphlcEontias. 



There is a secondary spectacle formed by the fused transparent lids. 

 In Ablepharus this is surrounded by a ring of scales ; in Typhlceontias this 

 is absent. 



Fig. 437. — Zonosaurus. 



Fig. 438. — Eremius. 



Fig. 439. — Mabuija. 



The lower lid is mobile. In Zonosaurus the scaly lower lid rises to meet 

 the upper lid ; in Eremias the central scales are transparent ; in Mabuya 

 the central scales are lacking (after Angel). 



Fig. 440. — Anolis lucius. 



Fig. 441. — Anolis argenteolus. 



The mobile lower lid has semi-transparent scales (3 in .4. lucius, 2 in 

 A. argenteolus) with a black bordered edge (Williams and Hecht). 



exceptional for eyelids to be absent, as in Pachydactylus maculatus, one of 

 the geckos wherein they are represented only by a thickened dermal fringe 

 around the periphery of the eye. 



When the lower Hd i.s mobile and opaque, a transparent nictitating 

 membrane is formed from a vertical fold of the conjunctiva at the 

 nasal corner of the palj^ebral aperture which can be swept across the 

 cornea from the nasal to the temporal side. Moisture and lubri- 

 cation are usually attained by a lacrimal gland with several con- 

 tractile ducts at the temporal canthus and a large harderian gland 



