17 



Of these orders only the last three are represented with 

 us, and, omitting the Ophidia, as outside the scope of this 

 paper, we now will take up the remaining two orders. 



Order Lacertilia. Lizards. 



Lizards have in common with snakes imbricated scales 

 (the chameleons excepted). The vent is a cross-slit ; the 

 skull bones are separate ; the jaws toothed ; the dorsal 

 vertebrae and ribs are movable, not grown together as in 

 the turtles. The tongue is free and projectile to a greater 

 or less degree, but is not used for tactile purposes as much 

 as by snakes, owing to the better eyesight of lizards. 



Lizards differ from snakes in having non-dilatable 

 mouths ; they have four, two or no limbs ; a shoulder 

 girdle ; long tails ; mostly three eyelids (including the so- 

 called nictitating membrane), and a tympanum. A pe- 

 culiarity of lizards is, that the tails in a great number of 

 them are very brittle and easily snap off. This is due to the 

 fact that there is a thin septum in each vertebra which 

 does not ossify, the break occurring across a vertebra, not 

 between two of them, as is generally supposed. Tails 

 broken off can be reproduced in many species. 



The vertebrae are generally proccelus and very numer- 

 ous, the transverse processes are short and rudimentary. 

 There are never more than two sacral nor more than nine 

 cervical vertebrae. The quadrate bone articulates with the 

 skull. 



The lungs are equal in size, except in the snake-like 

 forms in which the right lung is the larger, while the left 

 sometimes becomes rudimentary. 



Lizards are terrestrial or arboreal in their habits, pre- 

 ferring warm, dry localities, the only known exception is 

 the seaweed-eating leguan of the Gallapagos Islands. 1 The 

 only lizard known to be venomous is the Gila monster 

 {Heloderma suspectum) of the Sonoran Region of North 

 America. 



1 See Darwin, " Voyage of the Beagle." 



