REPTILIAN LIVERIES 167 



by the interposition of white pigment along the centre of 

 a dark median band, so that a white stripe and two black 

 stripes result : or the process may be reversed. A primi- 

 tive white stripe running down the centre of the back may 

 broaden, and at the same time develop dark pigment 

 down its centre, thus forming a single dorsal black stripe 

 flanked by a pair of white stripes. 



That the colour, number, and distribution of these 

 stripes are largely determined by the needs of the environ- 

 ment, that is to say by the need that the body of each 

 particular individual shall harmonise as much as possible 

 with its background, seems evident enough. Thus, if 

 we start with a species like the wall-lizard, wherein the 

 young are normally marked by many stripes, it will be 

 found that in individuals frequenting sandy districts dotted 

 with sparse tufts of grass there is a tendency to an in- 

 crease in the number of stripes, which may increase from 

 six to eight, or eleven. On the other hand, in neighbouring 

 areas, where the vegetation is more abundant, the number 

 of stripes is usually from seven to nine, and these show a 

 tendency to break up into spots on the hind part of the 

 back. As we pass into open forest with much under- 

 growth, the lateral stripes fade, while the others dissolve 

 into spots which have a tendency to disappear in the loins 

 of old individuals. 



Again, in races inhabiting open tableland with scattered 

 spiny shrubs and hedges, the young form with six stripes 

 and pale spots on the dark bands passes into a cross- 

 barred type. Finally, in similar localities, but with more 

 mixed vegetation, all the lines become broken up into 

 spots in addition to those which existed in the intermediate 

 dark intervals. 



There seems Httle doubt but that these stripes cannot 



