REPTILES 



359 



fined to the thickened rim of the pupillary margin (Mann, 1929). This 

 vascular pattern may to some extent be obscured by the pigment of 

 the multicoloured iris {Agama) but stands out in prominent relief in 

 those irides provided with a guanine layer on which, indeed, the vessels 

 may cast shadows ; it is to be noted that the general arrangement of 

 deep circumferential arteries and superficial radial veins, found 

 commonly among Sauropsida. is completely different from the ichthyo- 

 psidan j^lan. 



The angle of the anterior chamber is occujoied by a loose jDectinate 

 ligament bridging over the space between the cornea and the anterior 



Agama 



Fig. 425. — The Pupils of a Xoctviinal Gecko. 



The Tokay gecko, so called from its chirping cry " Tuk-kaa." On the 

 left, the pupil contracted by bright light, showing its reduction to a slit with 

 three stenopa?ic openings. On the right, the wide hexagonal pupil in dark- 

 ness photographed by infra-red light. (New York Zoological Society ; photo- 

 graphs by Sam Dunton ; from the Illustrated London Xexcs.) 



chamber, ■\\hile a ciliary sinus, ^ venous in nature but usually devoid 

 of blood, runs circumferentially around the region of the angle 

 separated from the sclera by fibres of the ciliar}^ muscle (Lauber, 1931) 

 (Figs. 423-4). 



The ^Ji<^Ji7 in diurnal lizards is usually round and relatively 

 immobile, in nocturnal lizards extremely active and contracting to a 

 slit-shape (with the exception of the Gila monster, Helodenna, wliich 

 has circular pupils, Walls, 1934). Of the latter tjq)e, a typical slit- 

 shaped pupil is seen in the Mexican night lizard, Xanfusia (Kallmann, 

 1932-33). In this class, however, the most interesting is the pupil of 

 the nocturnal geckos (Fig. 425) which is somewhat reminiscent of that 

 seen in the dogfish, ScijlUorhinus (Fig. 313) and in some rays, 

 (Fig. 312). The diurnal geckos, like the great majority of lizards, have 

 a round pupil, remaining circular on contraction and little if at all 

 affected by sunlight or drugs, but in the nocturnal types in diffuse 



1 Analogous to the canal of Schlemm. 



Heloderma ._ 



