198 ANIMAL FORMS 



ebb. Almost all the movements and operations of the body 

 appear to be carried on by the animal with little apparent 

 thought. Their acts, like most of the animals below them, 

 are said to be instinctive ; yet they are sufficiently well done 

 to enable the animal to procure its food, avoid its enemies, 

 and lead a successful life. As is true of other animals, the 

 ability of the reptile to cope with its surroundings depends 

 to a great extent upon the keenness of one or all of its or- 

 gans of special sense. In the reptiles the sense of sight is 

 perhaps sharpest, but there is considerable variation in this 

 respect. Eyelids are present in all except the snakes, to- 

 gether with a third, known as the nictitating membrane, a 

 thin, transparent fold located at the inner angle of the eye, 

 over which it is drawn with great rapidity. In the snakes 

 eyelids are absent, giving the eye its characteristic stare. 

 Furthermore, their sense of sight, except in a few tree-dwell- 

 ing species, appears to be defective, the majority depending 

 largely upon the sense of touch. 



In all the vertebrates a very peculiar organ known 

 as the pineal gland or eye is situated on the roof of the 

 brain. In several lizards its position is indicated by a trans- 

 parent area in one of the plates of the head, and by an 

 opening in the bones of the roof of the skull. In young 

 reptiles, and especially in one of the New Zealand lizards 

 (Hatteria, Fig. 119), its resemblance to an eye is decidedly 

 striking. Lens, retina, pigment, cornea, are all present 

 much as they are in some of the snails, but they finally 

 degenerate more or less as the animal reaches maturity. 

 It is a general belief that it represents the remnant of an 

 organ of sight, a third eye, which looked out through the 

 roof of the skull in some of the ancient vertebrates. 



With the possible exception of the few species of reptiles 

 which produce sounds, probably to attract their mate, the 

 sense of hearing is not particularly well developed. The 

 senses of smell and taste are also comparatively feeble. The 

 latter sense is located in the tongue, which is also popularly 



