VIPERS AND PIT VIPERS 



gland to the wound which their sharp end has made 

 in some hostile or edible creature. The reduction of 

 the poison fangs and their tubular, not merely grooved, 

 structure is a mark of the viperine dentition. More- 

 over, this particular viper has a little pit on the side 

 of the face, as has the rattlesnake, from which char- 

 acter it is known as a pit viper, a distinction from the 

 common viper of this country and its allies, which are 

 perfect as vipers, but have no pit. This snake haunts 

 the leafy branches of trees, and, as we suppose, in 

 accordance with that habit, its uniform hue hides it 

 when motionless. This same shade of green is not 

 uncommon among reptiles. It is to be seen, for ex- 

 ample, in the European green lizard, and in a very 

 beautiful gecko from Madagascar, which has the name 

 of Phelsuma madagascariensis, in various chamaeleons, 

 and in other forms. The green is of the same timbre 

 in all of them. This little viper is therefore doubly 

 armed to hold its own. It can escape observation by 

 its harmonious colouring, harmonious, that is to say, 

 with leafy or grassy surroundings, and it can give a 

 thoroughly good account of itself if detected. 



ORDER CHELONIA 



The tortoises and turtles form an assemblage about 

 the limits of which there can be no possible mistake. 

 They are encased more or less completely in a bony 

 box, which is generally overlaid by epidermic scales, 

 quite comparable with those of lizards. The bony box 

 is produced by ossifications within the skin, and has, 

 of course, nothing to do with the skeleton proper, 

 although its bones are often fused with bones of the 

 true skeleton. The Chelonia also have toothless jaws, 

 the want of teeth being to some extent compensated 

 by the existence of a horny sheath to the jaws, which 

 is exactly comparable to the bird's beak. 



265 



