192 ZOOLOGY. 



The poisonous snakes stand lowest in the series; they are 

 succeeded by the striped snake, milk adder, and by the 

 boas, which attain a length of five metres; while the ana- 

 conda grows eight metres long. 



Orders. Lacertilia. — Most lizards have cylindrical bodies, 

 usually covered with small overlapping scales, with a long, 

 slender tail, and generally two pairs of feet, the toes long 

 and slender, and ending in claws. They run with great 

 rapidity, and are active, agiJe creatures, adorned with bright 

 metallic colors, in some cases green or brown, simulating 

 the tints of the vegetation or soil on which they live; some 

 are capable of changing their color at will, as in the chame- 

 leon and Anolis; this is due to the fact that the pigment 

 cells (chromatophores) are under the influence of the vol- 

 untary nerves. 



In many lizards (Lacerta, Iguana, and the Geckos), the 

 middle of each caudal vertebra has a thin cartilaginous par- 

 tition, and it is at this point that the tails of these lizards 

 break off so easily when seized. In such cases the tail is 

 renewed, but is more stumpy. 



Both jaws are provided with teeth, while some have them 

 developed on the bones of the mouth. The teeth are usu- 

 ally simple, sharp, conical, as in most lizards, including the 

 Monitor, or they are' flattened, blade-like, with serrated 

 edges, as in the Iguana, or as in Cydodus they are broad, 

 adapted for crushing the food. Most lizards prey on in- 

 sects; some live on plants. The eyelids are well-developed 

 except in the Geckos, in which the lids are modified some- 

 what, as in the snakes, to form a transparent skin over the 

 cornea of the eyes. The tongue is free and long, some- 

 times forked; in the iguana it ends in a horny point. 



While the limbs are usually present, one or the other 

 pair may in rare cases (in Pseudojms the fore feet are 

 wanting; in Chirotes the hind feet are absent) be absent, 

 or as in Amphisbmna and its allies the feet are entirely 

 wanting. 



Lizards lay their eggs in the sand or soil. The iguana 



