622 REPTILES 



(D) Squamates 



See also pages: 251 Figs. 99, 100 



56, 61-3, 161-2, 165-8, 176, 178, 216, 254 254, 270, 272-3, 279-83, 438, accommo- 



visual cells, transmutation dation, refraction 



72, 169-70, 206 vision 270-1, 274 scleral ossicles 



78 rhodopsin 289,293-5,321 visual fields 



101-2 zapfensubstanz 299-300 binocularity 



134-5, 138 origin, relationships 306-7 eye movements 



145, 215, 342 habits 339-40 parietal eye 



157, 161-2, 220-1, 224-5, 256-7 pupil 344-5 movement perception 



174 acuity adaptations 423-4 adnexa 



185-8 fovea 438 amphibious adaptations 



191-6, 199-203 yellow filters and their 450-1, 454-9 spectacle 



significance 465-7,495-7,519-20 color vision 



223 Fig. 88 524-6, 538-43 dermal color changes 



230 eyeshine 545-9 coloration of eye 



The twenty families of lizards and the eleven families of snakes are 

 scattered around the globe in the temperate and torrid zones. Nothing 

 in biology is more certain than that the snakes were derived from lizards, 

 and the closeness of the relationship is indicated by the placement of 

 the two groups in a single order, the Squamata (meaning 'with scales') 

 as suborders, the Lacertilia (lizards) and the Ophidia (snakes). 



Lizards — The lizards exhibit a greater number of the ocular features 

 listed earlier as 'reptilian' than do any other living reptiles. This does 

 not mean however that this combination of features was evolved first by 

 this relatively recent group — the absence of certain of them in turtles, 

 crocodilians, and Sphenodon has been explained above as owing to sec- 

 ondary nocturnality, to a special importance of the iris in accommo- 

 dation, etc. We may be sure that the lizards have only preserved, not 

 assembled, the complex here characterized (pp. 607-8) as 'reptiUan'; 

 for, we shall encounter the entire complex again in the birds, which got 

 it not from the lizards, but from much older reptiles — the ornithischian 

 dinosaurs which were the birds' immediate ancestors. 



The lacertilian eye is relatively large and characteristically 'diurnal' 

 in make-up, and has certainly been so for as long as there have been 

 lizards — and longer: If we could take the eye of Sphenodon in hand 

 and undo all of the things which have been done to make it suitable for 

 dim-light activity, we should find ourselves holding an essentially lacer- 

 tilian eye, representing not only the eye of the ancient diurnal rhyncho- 

 cephalians but probably that of the eosuchians as well (see Fig. 60, p. 



