238 SNAKES. 



as well as by the absence of horns. The upper surface of the head is covered with 

 scales, and the keeled scales of the body form from twenty-five to thirty -five rows. 

 The common desert saw-viper, or, as it is called in Egypt, eja (Echis carinata), 

 attains a length of about 2 feet ; and has the keels on the lateral scales of the body 

 strongly serrated. In colour it varies from pale buff to greyish, reddish, or pale 

 brown on the upper-parts, with three series of whitish spots edged with dark 

 brown, in addition to which there may be a dark brown zigzag band along each 

 side, while the head is ornamented with a cross or arrowhead mark; and the 

 under-parts are whitish, either with or without brown dots. This species inhabits 

 the desert regions of Northern Africa, South-Western Asia, and India, being 

 replaced in Arabia and Palestine by E. colorata. 



The most remarkable peculiarity of this viper (which, however, it may possess 

 in common with the horned vipers, since the scales of the latter have a similar 

 structure) is its power of making a curious, prolonged, almost hissing sound, 

 produced by rubbing the folds of the sides of the body one against another, when 

 the serrated lateral scales grate together. That this is the true cause of the 

 sound may be proved by twisting the body of a dead specimen, and thus causing 

 friction between the scales. Sir J. Fayrer writes that this species is a very fierce 

 and vicious viper ; it throws itself into an attitude of defence and offence, coiled 

 up like a spring, rustling its carinated scales as it moves one fold of the body 

 against another. It is aggressive, and does not wait to be attacked before darting 

 its head and body at its enemy, the mouth wide open, and the long fangs 

 vibrating, thus presenting a most menacing appearance. It is very poisonous, 

 and there can be little doubt that it destroys many human lives, as men are 

 much more exposed to contact with this species than with Russell's viper. 



The dreaded rattle-snakes of the New World are our first repre- 

 sentatives of the subfamily of pit- vipers (Crotalince), which, are 

 common to Asia and America, and are characterised by the presence between 

 the nostril and the eye of a deep pit in each loreal shield, the physiological 

 significance of which is still unknown. All have triangular broad heads, and 

 short thick bodies. The Asiatic representatives of the group are less deadly 

 serpents than their American relatives ; while the only vestige of the rattle of 

 the latter to be found in the former is a small horny spine at the end of the tail 

 of one species. Many of the Indian species are arboreal in their habits ; their 

 coloration assimilating to that of the foliage and boughs among which they 

 dwell. As regards their geographical distribution, pit-vipers present a curious 

 similarity to bears and deer ; and since they are most abundant in the Oriental 

 region, and also more numerous in North than in South America, Mr. Wallace is 

 of opinion that the group originated in the Indo-Chinese countries, and thence 

 spread north-eastwards to North America, and so onward to the southern half of 

 the New World, which area, having been the last to receive the group, has not 

 had time, in spite of its extreme fitness for reptilian life, to allow it to attain its 

 full development. 



The rattle-snakes are sufficiently distinguished from their allies by the 

 jointed horny appendage at the end of the tail from which they derive their name. 

 In the young rattle-snake the tail terminates in a somewhat nail-like " button," 



