THE ORDER LACERTILIA 11 



obtain all the information required for our purpose 

 from these two families. 



Most lizards are found on examination to possess 

 two pairs of limbs, an anterior pair and a posterior 

 pair, all these limbs being built up on the typical 

 vertebral type, such as is commonly studied in the 

 frog, and known as the pentadactyloid type. Some 

 species, however, show no indication of any external 

 limbs at all, giving them a snake-like appearance to 

 the eye, an example of which is to be seen in the 

 slow-worm. The great majority have eyelids, which 

 are movable, a feature which distinguishes these 

 members from snakes which have no movable eye- 

 lids. The external covering in most is in the form 

 of scales. The great interest of the group is their 

 immense variation. " They exhibit a great, almost 

 endless, variety in shape, size, and structure, in 

 adaptation to their surroundings. Most of these 

 modifications are' restricted to the external organs, 

 or rather to those which come into direct contact 

 with the outer world, namely, the skin, the limbs, 

 the tail, or the tongue. The majority are terrestrial, 

 but there are also semi-aquatic forms. There are 

 climbing, swiftly running, and even flying forms, 

 whilst others lead a subterranean life like earthworms. 

 Most of them live on animal food, varying from tiny 

 insects and worms to birds and mammals, while 

 others live on vegetable diet. According to this 

 diet, the teeth and the whole digestive tract are 



