REPTILES 



355 



arteries and suj)erficiaJ radial veins in jylace of the reverse arrangement in 

 IcJithyojJsida. 



An esseniiaUy simjAe retina tvith a cone 2^opidation in diurnal 

 species and a rod jioiJidation in those with nocturnal habits ; each type 

 of cell may be single or donble and each may contain an oil-drop)let. 



THE LACERTILIAN EYE 



there are some 20 families extant, i essentially 



Of LIZARDS 



inhabitants of the warmer regions of the earth ; they are active, agile 

 animals, with an exoskeleton of scales often beautifully coloured, 

 feeding usually on insects, worms and other small animals, although 



Fig. 419. — The Head of the Lizard, Lacerta muralis (X 3-5) 

 (Katharine Tanslev). • 



Fig. 420. — The Chameleon (photograph by Michael Soley) 



1 Including the true lizards of the Old Vv'orld deserts, the skinks, the geckos, the 

 monitors (or dragons), iguanas, agamid lizards, Gila monsters, glass snakes, limbless 

 slow-worms and the chameleon. 



