SCALED REPTILES—SNAKES. 427 



accordance with their chiefly nocturnal habits, the eye has its pupil in the 

 form of a vertical slit. Only a few vipers climb, and none are aquatic ; while, 

 so far as present information goes, all give birth to their young in a fully 

 developed state without laying eggs. In almost all countries popular report 

 declares that the females of many species receive their young into their 

 mouth when alarmed, whence they apparently pass down the throat ; and 

 although many attempts have been made to discredit such statements, it is 

 diflicult to believe that they have not some foundation of truth. 



Of the two sub-families into which these snakes are divided by zoologists, 

 the typical vipers, or Vijyerinin, are confined to the Eastern Hemisphere, and 

 are characterised by the absence of pits or depressions in the pair of head- 

 shields known as the loreals. The common British viper ( Fipera herus) is 

 the most familiar representative of the typical genus, all the members of 

 which have two longitudinal series of shields on the under surface of the tail, 

 while the scales on the body are keeled and arranged in from nineteen to 

 thirty-one straight longitudinal rows, and the upper surface of the head is 

 invested either with relatively small shields or with scales. There are about 

 twenty different kinds of true vipers, and these are distributed over the greater 

 part of the Old World, although there are none in Australasia or Madagascar,' 

 and only one in India. The common viper enjoys a very wide geographical 

 distribution, extending from the Arctic Circle to Spain and Portugal, and 

 from the latter country eastwards to Siberia. It not unfrequently grows to 

 ten inches in length, and, like its kindred, is partial to warm sandy heaths. 

 The sand-viper {V. ammodytes) of Southern and Eastern Europe is remark- 

 able for having a flexible horn-like and scaly appendage surmounting the tip 

 of the muzzle, the use of which has not yet been explained. To the genus 

 Bitia belongs the dreaded African puff'-adder {B. arietans), in which the 

 head is broader and more distinctly 

 triangular than in any of its kindred. 

 As this noxious serpent has a habit 

 of lying with only its head exposed, 

 it is frequently not noticed by men 

 and animals until too late ; and 

 it is consequently responsible for 

 many deaths. Even large mam- 

 mals are said to succumb very 

 speedily to the bite of this loath- 

 some Tuonster. The name of puff- 

 adder is derived from the habit 

 possessed by this snake of blowing 

 itself out with air when excited. Fig. 26.— Puff-Addeb (Bitis arietans). 



Nearly allied to the true vipers are 



the horned vipers of the genus Cerastes, so named from the presence of a pair 

 of scaly horns situated above the eyes of the males, and in some species in 

 the females also. The scales, too, are arranged in oblique instead of straight 

 series. Both species of the genus are inhabitants of those parts of Northern 

 Africa lying to the eastward of Morocco, but one is also found in Arabia. 

 They grow to about a couple of feet in length, and assimilate remarkably in 

 coloration to the sandy deserts they frequent. They may be often seen so 

 deeply buried in the sand that only the head and a portion of the neck pro- 

 ject above the surface. Another nearly allied genus is that of the saw-vipers, 

 or Echis ; these snakes being distinguished from the last by the absence of 



