140 STORY OF THE REPTILES 



lizards have the eyelids covered bj the outside skin 

 so that they can not be moved. 



In the chameleons the eye-opening may be round 

 and is drawn up Uke an old-fashioned purse — as if a 

 draw-string were around it. One eye can be turned 

 forward while the other is rolled backward, so that 

 the creature can really look two ways at once. This 

 peculiarity is not known anywhere else, though birds 

 and many mammals see two ways at once because 

 one eye is on each side of the head. But both eyes 

 move forward or backward together. 



We have noted that Tuatera has beneath its skull 

 the remnants of a third eye, which was once central 

 in the top of the head. Some other lizards show 

 hints of the same thing ; and in the growth of the 

 young of all, there is in the roof of the skull a place 

 that is slow to close. This has been supposed by 

 some to be the vestige of the former opening of this 

 third eye. 



The fact that reptiles are so odorous argues that 

 they Smell, if there were no other means of infer- 

 rinfi^ it. All breathe air throufi^h the nostrils which 

 of course, unlike those of lislies, enter the mouth. 

 In the crocodilians these enter far back, and there is a 

 soft flap of the palate which drops down in front of 

 them so that the creature can keep its mouth open 

 under water and not get strangled ; and at the ex- 

 treme end of the snout, where the nose opens outward, 

 are valves which can be closed to keep the water out. 



In the water-snakes, also, the nostrils open near 

 the tip — really on the upper side of the snout — so 



