LIZARDS 53 



not reproduced, the axis being replaced by a continuous 

 rod of calcified tissue. The scaling on the reproduced 

 portion often differs from that of the uninjured part. 



The arrangement of the teeth is of importance in the 

 classification of lizards ; for instance, two great families, 

 the Agamidce of the Old World, and the Iguanidce of the 

 New World, being simply distinguished by their dentition, 

 this being acrodont in the former, pleurodont in the 

 latter (see p. 6, fig. i). In one family only, the 

 H elodermatidce , containing a single genus, are the teeth 

 fang-like, and provided with a groove which conveys a 

 poisonous fluid secreted by special glands. 



The skin, which is shed periodically, mostly in flakes, 

 but sometimes entire, is invariably covered with scales 

 or tubercles ; in the worm-like Amphisbcenidce, however, 

 these scales are soft, and appear more as divisions of the 

 integument. 



The food of lizards varies ; the majority are insecti- 

 vorous, some, however, such as the large Monitors, feed 

 on birds, small mammals, and eggs, whilst others, such as 

 many of the Iguanas, are mainly vegetarian. 



As a general rule lizards lay eggs, which are deposited 

 in mould or sand : a few, such as the Common Lizard, 

 the Slow-worm and most of the Skinks, bring forth their 

 young alive. 



The Geckos, family Geckonid^, represented in all the 

 tropical and warmer parts of the world, have usually 

 dilated digits, the digital pads serving as adhesive organs, 

 by means of which they can stick to smooth surfaces ; in 

 some, however, especially in those living in barren regions. 



